bpo-40275: Use new test.support helper submodules in tests (GH-21151)

Use new test.support helper submodules in tests:

* distutils tests
* test_buffer
* test_compile
* test_filecmp
* test_fileinput
* test_readline
* test_smtpnet
* test_structmembers
* test_tools
diff --git a/Lib/test/test_readline.py b/Lib/test/test_readline.py
index 67ee9b7..de573be 100644
--- a/Lib/test/test_readline.py
+++ b/Lib/test/test_readline.py
@@ -10,7 +10,9 @@
 import sys
 import tempfile
 import unittest
-from test.support import import_module, unlink, temp_dir, TESTFN, verbose
+from test.support import verbose
+from test.support.import_helper import import_module
+from test.support.os_helper import unlink, temp_dir, TESTFN
 from test.support.script_helper import assert_python_ok
 
 # Skip tests if there is no readline module