Fixes serialization of delete activity

bookwyrm/models/activitypub_mixin.py

@@ -369,16 +369,6 @@ class OrderedCollectionMixin(OrderedCollectionPageMixin):
         if self.user.local and broadcast:
             self.broadcast(activity, self.user)
 
-    def to_delete_activity(self, user):
-        """notice of deletion"""
-        return activitypub.Delete(
-            id=self.remote_id + "/activity",
-            actor=user.remote_id,
-            to=["%s/followers" % user.remote_id],
-            cc=["https://www.w3.org/ns/activitystreams#Public"],
-            object=self.remote_id,
-        ).serialize()
-
 
 class CollectionItemMixin(ActivitypubMixin):
     """for items that are part of an (Ordered)Collection"""