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.
diff --git a/Lib/test/test_ucn.py b/Lib/test/test_ucn.py
index 1e07f66..8febf0a 100644
--- a/Lib/test/test_ucn.py
+++ b/Lib/test/test_ucn.py
@@ -233,8 +233,5 @@
         )
 
 
-def test_main():
-    support.run_unittest(UnicodeNamesTest)
-
 if __name__ == "__main__":
-    test_main()
+    unittest.main()