Delete spam users from database

[carakey]

There are about 80K users in the OJS database, according to a blank user search in the dashboard. All but a few hundred are probably spam accounts. The spam blocking strategies (#45) are working well and new fake accounts have stopped. These existing spam accounts should be deleted, for storage, performance, and resolving potential conflicts.

Spam accounts shouldn't have been able to complete the email verification step, so hopefully they can be picked out easily, e.g. no roles in any journals.