Refs #34986 -- Removed redundant CustomChoicesTests.test_timezone_unsupported().

This test relied on the behavior of subclassing `datetime.timezone`
which is not permitted by the C-extension version of CPython's
`datetime` module. This restriction isn't enforced by the pure
Python version, nor by PyPy.

See https://github.com/python/cpython/issues/112451

It's not critical, and doesn't test any Django behavior, so just
remove it.

tests/model_enums/tests.py

@@ -316,13 +316,6 @@ class CustomChoicesTests(SimpleTestCase):
             class Boolean(bool, models.Choices):
                 pass
 
-    def test_timezone_unsupported(self):
-        msg = "type 'datetime.timezone' is not an acceptable base type"
-        with self.assertRaisesMessage(TypeError, msg):
-
-            class Timezone(datetime.timezone, models.Choices):
-                pass
-
     def test_uuid_unsupported(self):
         with self.assertRaises(TypeError):