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_numeric_tower.py

@@ -5,7 +5,6 @@ import random
 import math
 import sys
 import operator
-from test.support import run_unittest
 
 from decimal import Decimal as D
 from fractions import Fraction as F
@@ -199,8 +198,5 @@ class ComparisonTest(unittest.TestCase):
                 self.assertRaises(TypeError, op, v, z)
 
 
-def test_main():
-    run_unittest(HashTest, ComparisonTest)
-
 if __name__ == '__main__':
-    test_main()
+    unittest.main()