Only broadcast distcp files (mosaicml#3130)

* filter

* remove metadata skip

composer/utils/checkpoint.py

@@ -288,15 +288,15 @@ def read_data(self, plan: LoadPlan, planner: LoadPlanner):
             receiver = dist.get_global_rank() != rank_in_first_replica
 
             # Send list of files to all ranks
-            file_list = [sorted(os.listdir(self.destination_path))]
+            file_list = [
+                file_name for file_name in sorted(os.listdir(self.destination_path)) if file_name.endswith('.distcp')
+            ]
             dist.broadcast_object_list(file_list, src=rank_in_first_replica, group=replicate_process_group)
             file_list = file_list[0]
             log.debug(f'List of files to broadcast: {file_list}')
 
             # Send each file to the appropriate rank
             for file_name in file_list:
-                if 'metadata' in file_name:  # All ranks already have the metadata file
-                    continue
                 if dist.get_local_rank() == 0:  # Only 1 rank per node needs to transfer file
                     full_path = os.path.join(self.destination_path, file_name)
                     log.debug(f'Transferring {full_path=}')