Revert "Gradient accumulation for TFTrainer (#9585)"

This reverts commit 3f40070c.

src/transformers/trainer_tf.py

@@ -638,9 +638,7 @@ class TFTrainer:
                 reduced_features = {
                     k: ft[: self.args.train_batch_size // self.args.n_replicas] for k, ft in features.items()
                 }
-                reduced_labels = {
-                    k: lbl[: self.args.train_batch_size // self.args.n_replicas] for k, lbl in labels.items()
-                }
+                reduced_labels = labels[: self.args.train_batch_size // self.args.n_replicas]
 
                 self.training_step(reduced_features, reduced_labels, nb_instances_in_global_batch)
 
@@ -652,13 +650,9 @@ class TFTrainer:
                     for k, ft in features.items()
                 }
 
-                labels = {
-                    k: tf.concat(
-                        [lbl[self.args.train_batch_size // self.args.n_replicas :], reduced_labels[k]],
-                        axis=0,
+                labels = tf.concat(
+                    [labels[self.args.train_batch_size // self.args.n_replicas :], reduced_labels], axis=0
                 )
-                    for k, lbl in labels.items()
-                }
 
             gradients = self.gradient_accumulator.gradients
             gradients = [