graph/db: refactor makeZombiePubkeys

Let the helper method only take the params it needs so that we dont need
to construct an entire models.ChannelEdgeInfo object to pass to it. This
will be useful later on.

graph/db/sql_store.go

@@ -1680,7 +1680,8 @@ func (s *SQLStore) DeleteChannelEdges(strictZombiePruning, markZombie bool,
 				}
 
 				nodeKey1, nodeKey2 = makeZombiePubkeys(
-					info, e1UpdateTime, e2UpdateTime,
+					info.NodeKey1Bytes, info.NodeKey2Bytes,
+					e1UpdateTime, e2UpdateTime,
 				)
 			}