Don't add a 'prev' key to m.room.member messages

synapse/handlers/profile.py

@@ -202,7 +202,6 @@ class ProfileHandler(BaseHandler):
 
             content = {
                 "membership": j.content["membership"],
-                "prev": j.content["membership"],
             }
 
             yield self.distributor.fire(

synapse/handlers/room.py

@@ -364,9 +364,6 @@ class RoomMemberHandler(BaseHandler):
             target_user_id, event.room_id
         )
 
-        if prev_state:
-            event.content["prev"] = prev_state.membership
-
         room_id = event.room_id
 
         # If we're trying to join a room then we have to do this differently