Don't return filename from upload

The uploader only needs to return the object_name of the uploaded
object. The filename is read directly from the input, so there's no need
to return it as well.

atst/models/attachment.py

@@ -25,12 +25,12 @@ class Attachment(Base, mixins.TimestampsMixin):
     @classmethod
     def attach(cls, fyle, resource=None, resource_id=None):
         try:
-            filename, object_name = app.uploader.upload(fyle)
+            object_name = app.uploader.upload(fyle)
         except UploadError as e:
             raise AttachmentError("Could not add attachment. " + str(e))
 
         attachment = Attachment(
-            filename=filename,
+            filename=fyle.filename,
             object_name=object_name,
             resource=resource,
             resource_id=resource_id,