Update various test modules to use unittest.main() for test discovery

instead of manually listing tests for test.support.run_unittest().

Lib/test/test_buffer.py

@@ -4283,9 +4283,5 @@ class TestBufferProtocol(unittest.TestCase):
         self.assertRaises(BufferError, memoryview, x)
 
 
-def test_main():
-    support.run_unittest(TestBufferProtocol)
-
-
 if __name__ == "__main__":
-    test_main()
+    unittest.main()