Use load balancer configuration, not load balancer id, in job-based LB removal logic

This is required to support RCv3.
Nice, shorter refactor, thanks!  

And apologies, there is no current test for this case - could you add a test that ensures that if load balancer 1 fails, then load balancer 2 is not added?  This is currently how it behaves, and the refactor looks equivalent, so not going to block this PR on it, but just wanted to make sure a test was in place.