Clean up stale if-guards for Python nonconformance that no longer applies.

I just tried removing a bunch of if api_implementation.Type() guards in
message_test.py, and a bunch of them just pass without specialization! The bugs
that used to cause trouble seem to be now fixed.

PiperOrigin-RevId: 711764185

python/google/protobuf/internal/message_test.py

@@ -2583,10 +2583,6 @@ class Proto3Test(unittest.TestCase):
     msg = map_unittest_pb2.TestMap()
     msg.map_int32_all_types[2].optional_string = 'bar'
 
-    if api_implementation.Type() == 'cpp':
-      # Need to keep the map reference because of b/27942626.
-      # TODO: Remove it.
-      unused_map = msg.map_int32_all_types  # pylint: disable=unused-variable
     msg_value = msg.map_int32_all_types[2]
     msg.Clear()