Remove clean rules

It's safe enough to just delete the build product directories.
diff --git a/Makefile b/Makefile
index 388e5f3..a4e8505 100644
--- a/Makefile
+++ b/Makefile
@@ -1133,8 +1133,8 @@
 endif
 endif
 
-clean: clean_libgpr clean_libgrpc clean_libgrpc_unsecure clean_libgpr_test_util clean_libgrpc_test_util clean_libgrpc++ clean_libgrpc++_test_util clean_libend2end_fixture_chttp2_fake_security clean_libend2end_fixture_chttp2_fullstack clean_libend2end_fixture_chttp2_simple_ssl_fullstack clean_libend2end_fixture_chttp2_simple_ssl_with_oauth2_fullstack clean_libend2end_fixture_chttp2_socket_pair clean_libend2end_fixture_chttp2_socket_pair_one_byte_at_a_time clean_libend2end_test_cancel_after_accept clean_libend2end_test_cancel_after_accept_and_writes_closed clean_libend2end_test_cancel_after_invoke clean_libend2end_test_cancel_before_invoke clean_libend2end_test_cancel_in_a_vacuum clean_libend2end_test_census_simple_request clean_libend2end_test_disappearing_server clean_libend2end_test_early_server_shutdown_finishes_inflight_calls clean_libend2end_test_early_server_shutdown_finishes_tags clean_libend2end_test_invoke_large_request clean_libend2end_test_max_concurrent_streams clean_libend2end_test_no_op clean_libend2end_test_ping_pong_streaming clean_libend2end_test_request_response_with_binary_metadata_and_payload clean_libend2end_test_request_response_with_metadata_and_payload clean_libend2end_test_request_response_with_payload clean_libend2end_test_request_response_with_trailing_metadata_and_payload clean_libend2end_test_simple_delayed_request clean_libend2end_test_simple_request clean_libend2end_test_thread_stress clean_libend2end_test_writes_done_hangs_with_pending_read clean_libend2end_certs clean_gen_hpack_tables clean_cpp_plugin clean_ruby_plugin clean_grpc_byte_buffer_reader_test clean_gpr_cancellable_test clean_gpr_log_test clean_gpr_useful_test clean_gpr_cmdline_test clean_gpr_histogram_test clean_gpr_host_port_test clean_gpr_slice_buffer_test clean_gpr_slice_test clean_gpr_string_test clean_gpr_sync_test clean_gpr_thd_test clean_gpr_time_test clean_murmur_hash_test clean_grpc_stream_op_test clean_alpn_test clean_time_averaged_stats_test clean_chttp2_stream_encoder_test clean_hpack_table_test clean_chttp2_stream_map_test clean_hpack_parser_test clean_transport_metadata_test clean_chttp2_status_conversion_test clean_chttp2_transport_end2end_test clean_tcp_posix_test clean_dualstack_socket_test clean_no_server_test clean_resolve_address_test clean_sockaddr_utils_test clean_tcp_server_posix_test clean_tcp_client_posix_test clean_grpc_channel_stack_test clean_metadata_buffer_test clean_grpc_completion_queue_test clean_grpc_completion_queue_benchmark clean_census_trace_store_test clean_census_stats_store_test clean_census_window_stats_test clean_census_statistics_quick_test clean_census_statistics_small_log_test clean_census_statistics_performance_test clean_census_statistics_multiple_writers_test clean_census_statistics_multiple_writers_circular_buffer_test clean_census_stub_test clean_census_hash_table_test clean_fling_server clean_fling_client clean_fling_test clean_echo_server clean_echo_client clean_echo_test clean_low_level_ping_pong_benchmark clean_message_compress_test clean_bin_encoder_test clean_secure_endpoint_test clean_httpcli_format_request_test clean_httpcli_parser_test clean_httpcli_test clean_grpc_credentials_test clean_grpc_fetch_oauth2 clean_grpc_base64_test clean_grpc_json_token_test clean_timeout_encoding_test clean_fd_posix_test clean_fling_stream_test clean_lame_client_test clean_thread_pool_test clean_status_test clean_sync_client_async_server_test clean_qps_client clean_qps_server clean_interop_server clean_interop_client clean_end2end_test clean_channel_arguments_test clean_credentials_test clean_alarm_test clean_alarm_list_test clean_alarm_heap_test clean_time_test clean_chttp2_fake_security_cancel_after_accept_test clean_chttp2_fake_security_cancel_after_accept_and_writes_closed_test clean_chttp2_fake_security_cancel_after_invoke_test clean_chttp2_fake_security_cancel_before_invoke_test clean_chttp2_fake_security_cancel_in_a_vacuum_test clean_chttp2_fake_security_census_simple_request_test clean_chttp2_fake_security_disappearing_server_test clean_chttp2_fake_security_early_server_shutdown_finishes_inflight_calls_test clean_chttp2_fake_security_early_server_shutdown_finishes_tags_test clean_chttp2_fake_security_invoke_large_request_test clean_chttp2_fake_security_max_concurrent_streams_test clean_chttp2_fake_security_no_op_test clean_chttp2_fake_security_ping_pong_streaming_test clean_chttp2_fake_security_request_response_with_binary_metadata_and_payload_test clean_chttp2_fake_security_request_response_with_metadata_and_payload_test clean_chttp2_fake_security_request_response_with_payload_test clean_chttp2_fake_security_request_response_with_trailing_metadata_and_payload_test clean_chttp2_fake_security_simple_delayed_request_test clean_chttp2_fake_security_simple_request_test clean_chttp2_fake_security_thread_stress_test clean_chttp2_fake_security_writes_done_hangs_with_pending_read_test clean_chttp2_fullstack_cancel_after_accept_test clean_chttp2_fullstack_cancel_after_accept_and_writes_closed_test clean_chttp2_fullstack_cancel_after_invoke_test clean_chttp2_fullstack_cancel_before_invoke_test clean_chttp2_fullstack_cancel_in_a_vacuum_test clean_chttp2_fullstack_census_simple_request_test clean_chttp2_fullstack_disappearing_server_test clean_chttp2_fullstack_early_server_shutdown_finishes_inflight_calls_test clean_chttp2_fullstack_early_server_shutdown_finishes_tags_test clean_chttp2_fullstack_invoke_large_request_test clean_chttp2_fullstack_max_concurrent_streams_test clean_chttp2_fullstack_no_op_test clean_chttp2_fullstack_ping_pong_streaming_test clean_chttp2_fullstack_request_response_with_binary_metadata_and_payload_test clean_chttp2_fullstack_request_response_with_metadata_and_payload_test clean_chttp2_fullstack_request_response_with_payload_test clean_chttp2_fullstack_request_response_with_trailing_metadata_and_payload_test clean_chttp2_fullstack_simple_delayed_request_test clean_chttp2_fullstack_simple_request_test clean_chttp2_fullstack_thread_stress_test clean_chttp2_fullstack_writes_done_hangs_with_pending_read_test clean_chttp2_simple_ssl_fullstack_cancel_after_accept_test clean_chttp2_simple_ssl_fullstack_cancel_after_accept_and_writes_closed_test clean_chttp2_simple_ssl_fullstack_cancel_after_invoke_test clean_chttp2_simple_ssl_fullstack_cancel_before_invoke_test clean_chttp2_simple_ssl_fullstack_cancel_in_a_vacuum_test clean_chttp2_simple_ssl_fullstack_census_simple_request_test clean_chttp2_simple_ssl_fullstack_disappearing_server_test clean_chttp2_simple_ssl_fullstack_early_server_shutdown_finishes_inflight_calls_test clean_chttp2_simple_ssl_fullstack_early_server_shutdown_finishes_tags_test clean_chttp2_simple_ssl_fullstack_invoke_large_request_test clean_chttp2_simple_ssl_fullstack_max_concurrent_streams_test clean_chttp2_simple_ssl_fullstack_no_op_test clean_chttp2_simple_ssl_fullstack_ping_pong_streaming_test clean_chttp2_simple_ssl_fullstack_request_response_with_binary_metadata_and_payload_test clean_chttp2_simple_ssl_fullstack_request_response_with_metadata_and_payload_test clean_chttp2_simple_ssl_fullstack_request_response_with_payload_test clean_chttp2_simple_ssl_fullstack_request_response_with_trailing_metadata_and_payload_test clean_chttp2_simple_ssl_fullstack_simple_delayed_request_test clean_chttp2_simple_ssl_fullstack_simple_request_test clean_chttp2_simple_ssl_fullstack_thread_stress_test clean_chttp2_simple_ssl_fullstack_writes_done_hangs_with_pending_read_test clean_chttp2_simple_ssl_with_oauth2_fullstack_cancel_after_accept_test clean_chttp2_simple_ssl_with_oauth2_fullstack_cancel_after_accept_and_writes_closed_test clean_chttp2_simple_ssl_with_oauth2_fullstack_cancel_after_invoke_test clean_chttp2_simple_ssl_with_oauth2_fullstack_cancel_before_invoke_test clean_chttp2_simple_ssl_with_oauth2_fullstack_cancel_in_a_vacuum_test clean_chttp2_simple_ssl_with_oauth2_fullstack_census_simple_request_test clean_chttp2_simple_ssl_with_oauth2_fullstack_disappearing_server_test clean_chttp2_simple_ssl_with_oauth2_fullstack_early_server_shutdown_finishes_inflight_calls_test clean_chttp2_simple_ssl_with_oauth2_fullstack_early_server_shutdown_finishes_tags_test clean_chttp2_simple_ssl_with_oauth2_fullstack_invoke_large_request_test clean_chttp2_simple_ssl_with_oauth2_fullstack_max_concurrent_streams_test clean_chttp2_simple_ssl_with_oauth2_fullstack_no_op_test clean_chttp2_simple_ssl_with_oauth2_fullstack_ping_pong_streaming_test clean_chttp2_simple_ssl_with_oauth2_fullstack_request_response_with_binary_metadata_and_payload_test clean_chttp2_simple_ssl_with_oauth2_fullstack_request_response_with_metadata_and_payload_test clean_chttp2_simple_ssl_with_oauth2_fullstack_request_response_with_payload_test clean_chttp2_simple_ssl_with_oauth2_fullstack_request_response_with_trailing_metadata_and_payload_test clean_chttp2_simple_ssl_with_oauth2_fullstack_simple_delayed_request_test clean_chttp2_simple_ssl_with_oauth2_fullstack_simple_request_test clean_chttp2_simple_ssl_with_oauth2_fullstack_thread_stress_test clean_chttp2_simple_ssl_with_oauth2_fullstack_writes_done_hangs_with_pending_read_test clean_chttp2_socket_pair_cancel_after_accept_test clean_chttp2_socket_pair_cancel_after_accept_and_writes_closed_test clean_chttp2_socket_pair_cancel_after_invoke_test clean_chttp2_socket_pair_cancel_before_invoke_test clean_chttp2_socket_pair_cancel_in_a_vacuum_test clean_chttp2_socket_pair_census_simple_request_test clean_chttp2_socket_pair_disappearing_server_test clean_chttp2_socket_pair_early_server_shutdown_finishes_inflight_calls_test clean_chttp2_socket_pair_early_server_shutdown_finishes_tags_test clean_chttp2_socket_pair_invoke_large_request_test clean_chttp2_socket_pair_max_concurrent_streams_test clean_chttp2_socket_pair_no_op_test clean_chttp2_socket_pair_ping_pong_streaming_test clean_chttp2_socket_pair_request_response_with_binary_metadata_and_payload_test clean_chttp2_socket_pair_request_response_with_metadata_and_payload_test clean_chttp2_socket_pair_request_response_with_payload_test clean_chttp2_socket_pair_request_response_with_trailing_metadata_and_payload_test clean_chttp2_socket_pair_simple_delayed_request_test clean_chttp2_socket_pair_simple_request_test clean_chttp2_socket_pair_thread_stress_test clean_chttp2_socket_pair_writes_done_hangs_with_pending_read_test clean_chttp2_socket_pair_one_byte_at_a_time_cancel_after_accept_test clean_chttp2_socket_pair_one_byte_at_a_time_cancel_after_accept_and_writes_closed_test clean_chttp2_socket_pair_one_byte_at_a_time_cancel_after_invoke_test clean_chttp2_socket_pair_one_byte_at_a_time_cancel_before_invoke_test clean_chttp2_socket_pair_one_byte_at_a_time_cancel_in_a_vacuum_test clean_chttp2_socket_pair_one_byte_at_a_time_census_simple_request_test clean_chttp2_socket_pair_one_byte_at_a_time_disappearing_server_test clean_chttp2_socket_pair_one_byte_at_a_time_early_server_shutdown_finishes_inflight_calls_test clean_chttp2_socket_pair_one_byte_at_a_time_early_server_shutdown_finishes_tags_test clean_chttp2_socket_pair_one_byte_at_a_time_invoke_large_request_test clean_chttp2_socket_pair_one_byte_at_a_time_max_concurrent_streams_test clean_chttp2_socket_pair_one_byte_at_a_time_no_op_test clean_chttp2_socket_pair_one_byte_at_a_time_ping_pong_streaming_test clean_chttp2_socket_pair_one_byte_at_a_time_request_response_with_binary_metadata_and_payload_test clean_chttp2_socket_pair_one_byte_at_a_time_request_response_with_metadata_and_payload_test clean_chttp2_socket_pair_one_byte_at_a_time_request_response_with_payload_test clean_chttp2_socket_pair_one_byte_at_a_time_request_response_with_trailing_metadata_and_payload_test clean_chttp2_socket_pair_one_byte_at_a_time_simple_delayed_request_test clean_chttp2_socket_pair_one_byte_at_a_time_simple_request_test clean_chttp2_socket_pair_one_byte_at_a_time_thread_stress_test clean_chttp2_socket_pair_one_byte_at_a_time_writes_done_hangs_with_pending_read_test
-	$(Q) $(RM) -r deps objs libs bins gens
+clean:
+	$(Q) $(RM) -rf deps objs libs bins gens
 
 
 # The various libraries