Deprecate TransfoXL (#27607)

* fix

* fix

* trigger

* Apply suggestions from code review

Co-authored-by: Lysandre Debut <hi@lysand.re>

* tic

* revert

* revert

---------

Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>
Co-authored-by: Lysandre Debut <hi@lysand.re>

utils/check_config_attributes.py

@@ -127,7 +127,6 @@ SPECIAL_CASES_TO_ALLOW.update(
         "SwitchTransformersConfig": True,
         "TableTransformerConfig": True,
         "TapasConfig": True,
-        "TransfoXLConfig": True,
         "UniSpeechConfig": True,
         "UniSpeechSatConfig": True,
         "WavLMConfig": True,