remove duplicate final snapshot path check (#636)

Summary:
Pull Request resolved: #636

Currently we check if two paths exist (one for snapshot path, and one for snapshot path/.snapshot_metadata) to determine whether to save final checkpoint or not. The first path is not necessary to check, so removing

Reviewed By: galrotem

Differential Revision: D51605223

fbshipit-source-id: bbee62ca74271a8a61317afe5dd2db3295978054

torchtnt/framework/callbacks/torchsnapshot_saver.py

@@ -245,12 +245,9 @@ def on_train_end(self, state: State, unit: TTrainUnit) -> None:
         )
 
         fs = get_filesystem(snapshot_path)
-        if fs.exists(snapshot_path):
-            if fs.exists(os.path.join(snapshot_path, SNAPSHOT_METADATA_FNAME)):
-                rank_zero_warn(
-                    "Final checkpoint already exists, skipping.", logger=logger
-                )
-                return
+        if fs.exists(os.path.join(snapshot_path, SNAPSHOT_METADATA_FNAME)):
+            rank_zero_warn("Final checkpoint already exists, skipping.", logger=logger)
+            return
 
         self._checkpoint_impl(
             state,