Remove unused `on_train_epoch_end` hook in accelerator (#9035)

CHANGELOG.md

@@ -166,6 +166,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Removed deprecated `connect_precision_plugin` and `connect_training_type_plugin` from `Accelerator` ([#9019](https://github.com/PyTorchLightning/pytorch-lightning/pull/9019))
 
 
+- Removed `on_train_epoch_end` from `Accelerator` ([#9035](https://github.com/PyTorchLightning/pytorch-lightning/pull/9035))
+
+
 ### Fixed
 
 - Ensure the existence of `DDPPlugin._sync_dir` in `reconciliate_processes` ([#8939](https://github.com/PyTorchLightning/pytorch-lightning/pull/8939))

pytorch_lightning/accelerators/accelerator.py

@@ -479,10 +479,6 @@ class Accelerator:
     def update_global_step(self, total_batch_idx: int, current_global_step: int) -> int:
         return self.training_type_plugin.update_global_step(total_batch_idx, current_global_step)
 
-    def on_train_epoch_end(self) -> None:
-        """Hook to do something on the end of an training epoch."""
-        pass
-
     def on_train_start(self) -> None:
         """Called when train begins."""
         return self.training_type_plugin.on_train_start()