Make use of the per-server jobqueue:s-queuesWithJobs key
Instead of tracking types/domains and hitting the cross-product
of those for periodic updates, only do them for queue that are
tracked as having non-abandoned jobs.
This saves CPU, makes undelaying/recycling more responsive,
and simplifies the code.
- Also remove unused batching logic from updateQueueServerChunk().
- Also rename some comments/vars from wiki => domain.