Issue #21741: Update 147 test modules to use test discovery.

I have compared output between pre- and post-patch runs of these tests
to make sure there's nothing missing and nothing broken, on both
Windows and Linux.  The only differences I found were actually tests
that were previously *not* run.
diff --git a/Lib/test/test_types.py b/Lib/test/test_types.py
index 11d9546..8cdecb0 100644
--- a/Lib/test/test_types.py
+++ b/Lib/test/test_types.py
@@ -1,6 +1,6 @@
 # Python test set -- part 6, built-in types
 
-from test.support import run_unittest, run_with_locale
+from test.support import run_with_locale
 import collections
 import pickle
 import locale
@@ -1172,9 +1172,5 @@
             self.assertEqual(ns, ns_roundtrip, pname)
 
 
-def test_main():
-    run_unittest(TypesTests, MappingProxyTests, ClassCreationTests,
-                 SimpleNamespaceTests)
-
 if __name__ == '__main__':
-    test_main()
+    unittest.main()