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

This is required to support RCv3.
Yes, the goal is indeed to have mostly separate code paths. #742 does that for adding to load balancers, a future ticket will do that for removing them.  I am keeping the `add_to_load_balancers` (but not `add_to_load_balancer`, which is being renamed to `add_to_clb`), and `remove_from_load_balancer`, because they have the appropriate API, so I hope that will require minimal changes.

I am keeping track of the overall progress on #739, and have tried to give some insight in to the plans there. This includes the plans for removing from load balancers: specifically, keep the API and name, but move the meat and potatoes of that function out, and have the function named `remove_from_load_balancer` just be responsible for picking a code path. One of the reasons for this choice is that it will hopefully be minimally impactful to mock-based testing.