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_telnetlib.py

@@ -393,9 +393,5 @@ class ExpectTests(ExpectAndReadTestCase):
         self.assertEqual(data, b''.join(want[:-1]))
 
 
-def test_main(verbose=None):
-    support.run_unittest(GeneralTests, ReadTests, WriteTests, OptionTests,
-                         ExpectTests)
-
 if __name__ == '__main__':
-    test_main()
+    unittest.main()