Job deletions are placed in an in-memory queue in batches of 100 jobs.
Between batches the Manager's job deleter would idle for 1 minute. Now,
once the in-memory queue has been emptied, the job deleter will wait
only 100ms before checking the database again.
This 100ms might not be necessary either, but I think it's nice to give
the Manager a bit of a breather before diving into another batch of
deletions.
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