Storage backends: removed unused Blob.filename attribute

Just use Blob.update_filename() instead.

pillar/api/file_storage_backends/abstract.py

@@ -90,12 +90,11 @@ class Blob(metaclass=abc.ABCMeta):
 
     def __init__(self, name: str, bucket: Bucket) -> None:
         self.name = name
+        """Name of this blob in the bucket."""
+
         self.bucket = bucket
         self._size_in_bytes: typing.Optional[int] = None
 
-        self.filename: str = None
-        """Name of the file for the Content-Disposition header when downloading it."""
-
         self._log = logging.getLogger(f'{__name__}.Blob')
 
     def __repr__(self):