Do not prune workers from queues that we don't listen to.

If the worker we are trying to prune does not belong to the queues we are listening to, we should not touch it. 

Attempt to prune a worker from different queues may result in an unknown class exception, since that worker could easily be even written in different language.

We are hitting this problem in production - half of our workers are written in Clojure and of course the Job class is different and not present in Ruby workers. If we run a Ruby worker and Clojure worker on same machine, Ruby workers start cleaning up workers after Clojure and dying.

All tests pass.