remove ChannelDB.add_channel_update (no longer needed after 46d8080c76)

electrum/channel_db.py

@@ -410,11 +410,6 @@ class ChannelDB(SqlDB):
             to_delete=to_delete,
         )
 
-    def add_channel_update(self, payload):
-        # called from add_own_channel
-        # the update may be categorized as deprecated because of caching
-        categorized_chan_upds = self.add_channel_updates([payload], verify=False)
-
     def create_database(self):
         c = self.conn.cursor()
         c.execute(create_node_info)