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_structmembers.py

@@ -140,8 +140,5 @@ class TestWarnings(unittest.TestCase):
             ts.T_USHORT = USHRT_MAX+1
 
 
-def test_main(verbose=None):
-    support.run_unittest(__name__)
-
 if __name__ == "__main__":
-    test_main(verbose=True)
+    unittest.main()