python: Update tuple handling pattern; returned by a delete() query.

This commit updates the pattern for dealing with tuples
returned by the delete() query.

The '(num_deleted, ignored) = ModelName.objects.filter().delete()'
pattern is preferred due to better readability.

We avoid the pattern '(num_deleted, _)' because Django uses _
for translation, which may lead to future bugs.

zerver/lib/retention.py

@@ -322,14 +322,14 @@ def delete_messages(msg_ids: List[int]) -> None:
 
 
 def delete_expired_attachments(realm: Realm) -> None:
-    attachments_deleted, _ = Attachment.objects.filter(
+    (num_deleted, ignored) = Attachment.objects.filter(
         messages__isnull=True,
         realm_id=realm.id,
         id__in=ArchivedAttachment.objects.filter(realm_id=realm.id),
     ).delete()
 
-    if attachments_deleted > 0:
-        logger.info("Cleaned up %s attachments for realm %s", attachments_deleted, realm.string_id)
+    if num_deleted > 0:
+        logger.info("Cleaned up %s attachments for realm %s", num_deleted, realm.string_id)
 
 
 def move_related_objects_to_archive(msg_ids: List[int]) -> None:

zilencer/views.py

@@ -194,10 +194,10 @@ def unregister_remote_push_device(
     validate_bouncer_token_request(token, token_kind)
     user_identity = UserPushIdentityCompat(user_id=user_id, user_uuid=user_uuid)
 
-    deleted = RemotePushDeviceToken.objects.filter(
+    (num_deleted, ignored) = RemotePushDeviceToken.objects.filter(
         user_identity.filter_q(), token=token, kind=token_kind, server=server
     ).delete()
-    if deleted[0] == 0:
+    if num_deleted == 0:
         raise JsonableError(err_("Token does not exist"))
 
     return json_success(request)