Update: ElectraDiscriminatorPredictions forward. (#5471)

`ElectraDiscriminatorPredictions.forward` should not need `attention_mask`.

src/transformers/modeling_electra.py

@@ -133,7 +133,7 @@ class ElectraDiscriminatorPredictions(nn.Module):
         self.dense_prediction = nn.Linear(config.hidden_size, 1)
         self.config = config
 
-    def forward(self, discriminator_hidden_states, attention_mask):
+    def forward(self, discriminator_hidden_states):
         hidden_states = self.dense(discriminator_hidden_states)
         hidden_states = get_activation(self.config.hidden_act)(hidden_states)
         logits = self.dense_prediction(hidden_states).squeeze()
@@ -518,7 +518,7 @@ class ElectraForPreTraining(ElectraPreTrainedModel):
         )
         discriminator_sequence_output = discriminator_hidden_states[0]
 
-        logits = self.discriminator_predictions(discriminator_sequence_output, attention_mask)
+        logits = self.discriminator_predictions(discriminator_sequence_output)
 
         output = (logits,)