revert black formatting to conform with lib style

transformers/modeling_seq2seq.py

@@ -43,13 +43,7 @@ class PreTrainedSeq2seq(PreTrainedModel):
         self.decoder = decoder
 
     @classmethod
-    def from_pretrained(
+    def from_pretrained(cls, encoder_pretrained_model_name_or_path, decoder_pretrained_model_name_or_path, *model_args, **kwargs):
-        cls,
-        encoder_pretrained_model_name_or_path,
-        decoder_pretrained_model_name_or_path,
-        *model_args,
-        **kwargs
-    ):
         r""" Instantiates an encoder and a decoder from one or two base classes
         of the library from pre-trained model checkpoints.