Remove redundant require_backward_grad_sync=False in sharded plugins (#10065)

Author: awaelchli

pytorch_lightning/plugins/training_type/sharded.py

@@ -73,7 +73,6 @@ def _setup_models_and_optimizers(
 
         optimizers = self._wrap_optimizers(optimizers)
         model = ShardedDataParallel(models[0], sharded_optimizer=optimizers, **self._ddp_kwargs)
-        setattr(model, "require_backward_grad_sync", False)  # TODO: needed?
         return [model], optimizers
 
     def _reinit_optimizers_with_oss(self, optimizers: List[Union[Optimizer, LightningOptimizer]]) -> List["OSS"]:

pytorch_lightning/plugins/training_type/sharded_spawn.py

@@ -64,7 +64,6 @@ def _setup_models_and_optimizers(
 
         optimizers = self._wrap_optimizers(optimizers)
         model = ShardedDataParallel(models[0], sharded_optimizer=optimizers, **self._ddp_kwargs)
-        setattr(model, "require_backward_grad_sync", False)  # TODO: needed?
         return [model], optimizers
 
     def _reinit_optimizers_with_oss(self, optimizers: List[Optimizer]) -> List["OSS"]: