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_select.py

@@ -75,9 +75,8 @@ class SelectTestCase(unittest.TestCase):
         a[:] = [F()] * 10
         self.assertEqual(select.select([], a, []), ([], a[:5], []))
 
-def test_main():
-    support.run_unittest(SelectTestCase)
+def tearDownModule():
     support.reap_children()
 
 if __name__ == "__main__":
-    test_main()
+    unittest.main()