Revert "Allow the same config in the auto mapping"

This reverts commit b1a7dfe.

src/transformers/models/auto/configuration_auto.py

@@ -389,13 +389,7 @@ def __getitem__(self, key):
         module_name = model_type_to_module_name(key)
         if module_name not in self._modules:
             self._modules[module_name] = importlib.import_module(f".{module_name}", "transformers.models")
-        if hasattr(self._modules[module_name], value):
-            return getattr(self._modules[module_name], value)
-
-        # Some of the mappings have entries model_type -> config of another model type. In that case we try to grab the
-        # object at the top level.
-        transformers_module = importlib.import_module("transformers")
-        return getattr(transformers_module, value)
+        return getattr(self._modules[module_name], value)
 
     def keys(self):
         return list(self._mapping.keys()) + list(self._extra_content.keys())