Remove checkpoints only on main process (#1974)

* Remove checkpoints only on main process

shutil.rmtree might throw errors if called on multiply processes. Make a call only on main process

* Apply style

src/accelerate/accelerator.py

@@ -2720,8 +2720,10 @@ def save_state(self, output_dir: str = None, **save_model_func_kwargs):
         os.makedirs(output_dir, exist_ok=True)
         if self.project_configuration.automatic_checkpoint_naming:
             folders = [os.path.join(output_dir, folder) for folder in os.listdir(output_dir)]
-            if self.project_configuration.total_limit is not None and (
-                len(folders) + 1 > self.project_configuration.total_limit
+            if (
+                self.project_configuration.total_limit is not None
+                and (len(folders) + 1 > self.project_configuration.total_limit)
+                and self.is_main_process
             ):
 
                 def _inner(folder):