[Routing] IPSet gets destroyed before ips are removed

On disarms, the scheduler fails with the error message ipset v6.38: The set with the given name does not exist (RedisRPC::RemoteException) coming from the RoutingRpcClient. This happens when the routing service destroys the ipset before the scheduler attempts to remove a subjects IP from the given set.

I think we should allow the call to remove an IP from an IPSet to fail if the IPSet does not exist.