Increase delete_users throughput again, this time with an index

apps/users/tasks.py

@@ -8,7 +8,7 @@ from users.models import UserProfile
 
 task_log = commonware.log.getLogger('z.task')
 
-@task(rate_limit='20/m')
+@task(rate_limit='40/m')
 def _delete_users(data, **kw):
     """Feed me a list of user ids you want to delete from the database.  This
     isn't a flag, it actually deletes rows."""

migrations/64-user-id-index.sql

@@ -0,0 +1,4 @@
+-- This needs to be added on your dev copies, but justdave already ran it on
+-- preview and production so I'm commenting it out here.
+
+-- ALTER TABLE addonlogs ADD KEY `user_id` (`user_id`);