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

This is required to support RCv3.
Non-blocking question - and apologies if this has been covered in other PRs already, but [this comment above](https://github.com/rackerlabs/otter/pull/738/files#r19703566) implies that picking which code path to use will happen in `remove_from_load_balancer` - is this going to happen in `delete_server` now instead?