Remove InvocationBehavior once we moved all the way to remoteCalls

[ktoso]

Once we have everything moved to remote calls, after #956 we should continue to move towards removal of behaviors in the call-paths.

Eventually removing the need to spawn behavior actors completely; and remove the need for the InvocationBehavior

[ktoso]

Likely not much remains here, I'll look into it

[yim-lee]

IIRC the remaining bit is in ClusterSystem.actorReady

[ktoso]

Not that much... It's a bit painful in assigning IDs as well, so might want to get this sorted soon :) I'll keep this on myself for now