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.

Lib/test/test_codecencodings_hk.py

@@ -19,8 +19,5 @@ class Test_Big5HKSCS(multibytecodec_support.TestBase, unittest.TestCase):
         (b"abc\x80\x80\xc1\xc4", "ignore",  "abc\u8b10"),
     )
 
-def test_main():
-    support.run_unittest(__name__)
-
 if __name__ == "__main__":
-    test_main()
+    unittest.main()