Make traced a top-level executable

- Make a little change to the Android blueprint generator, which
  makes it so that executables in the top-level BUILD.gn file
  don't get the perfetto_ prefix. This allows to get a binary
  in the Android.bp that is called just "traced" and ends up in
  /system/bin/traced
- Adds the consumer_cmd binary introduced by the previous change
  (Iccf88b7b1d2beb6a0750adafd86d92a0f563182d) to the blueprint.

Bug:
Change-Id: Ia091ba35f186a451c4c0e111fcc03a0d8decf816
diff --git a/BUILD.gn b/BUILD.gn
index 28f3fbb..9d9f9a1 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -20,8 +20,6 @@
     ":perfetto_tests",
     "src/ipc/protoc_plugin:ipc_plugin($host_toolchain)",
     "src/protozero/protoc_plugin($host_toolchain)",
-    "src/traced",
-    "src/tracing:consumer_cmd",
     "tools/ftrace_proto_gen:ftrace_proto_gen",
     "tools/proto_to_cpp",
   ]
@@ -56,4 +54,11 @@
       "src/tracing:tracing_benchmarks",
     ]
   }
+
+  executable("traced") {
+    deps = [
+      "gn:default_deps",
+      "src/traced",
+    ]
+  }
 }