Call the preexisting OnDisconnected methods for all disconnects

- This means that the preexisting OnDisconnected can now be called due
  to a timeout caused by a client connecting to another server in scaleout.
Yeah good point. It's the change we probably should have made in the first place. Simplifies everything and we don't need to explain what one overload does over the other or add any of this new task plumbing code.