fix: delete unnecessary function

Co-authored-by: Copilot <[email protected]>

Author: kitagry

gokart/gcs_obj_metadata_client.py

@@ -120,7 +120,7 @@ def _get_serialized_string(required_task_outputs: FlattenableItems[RequiredTaskO
         elif isinstance(required_task_outputs, dict):
             return {k: GCSObjectMetadataClient._get_serialized_string(v) for k, v in required_task_outputs.items()}
         elif isinstance(required_task_outputs, Iterable):
-            return list([GCSObjectMetadataClient._get_serialized_string(ro) for ro in required_task_outputs])
+            return [GCSObjectMetadataClient._get_serialized_string(ro) for ro in required_task_outputs]
         else:
             raise TypeError(
                 f'Unsupported type for required_task_outputs: {type(required_task_outputs)}. '