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_float.py

@@ -1299,18 +1299,5 @@ class HexFloatTestCase(unittest.TestCase):
                 self.identical(x, fromHex(toHex(x)))
 
 
-def test_main():
-    support.run_unittest(
-        GeneralFloatCases,
-        FormatFunctionsTestCase,
-        UnknownFormatTestCase,
-        IEEEFormatTestCase,
-        FormatTestCase,
-        ReprTestCase,
-        RoundTestCase,
-        InfNanTest,
-        HexFloatTestCase,
-        )
-
 if __name__ == '__main__':
-    test_main()
+    unittest.main()