also add a hard limit of 1000 users per job run so we do not clog the
scheduler
destroyer.destroy has a transaction and this can have some serious complications
with the open record set find_each has going
* Remove use of 0 in favor of `TrustLevel.levels[:newuser]`.
* Consolidate two tests into a single one.
* Test that disabling the feature works.
* Avoid loading full ActiveRecord object in test when we only need to
know the existence of the record.