Clean TF Bert (#9788)

* Start cleaning BERT

* Clean BERT and all those depends of it

* Fix attribute name

* Apply style

* Apply Sylvain's comments

* Apply Lysandre's comments

* remove unused import

src/transformers/models/ctrl/modeling_tf_ctrl.py

@@ -919,7 +919,7 @@ class TFCTRLForSequenceClassification(TFCTRLPreTrainedModel, TFSequenceClassific
         )
 
     # Copied from transformers.models.bert.modeling_tf_bert.TFBertForSequenceClassification.serving_output
-    def serving_output(self, output):
+    def serving_output(self, output: TFSequenceClassifierOutput) -> TFSequenceClassifierOutput:
         hs = tf.convert_to_tensor(output.hidden_states) if self.config.output_hidden_states else None
         attns = tf.convert_to_tensor(output.attentions) if self.config.output_attentions else None