FIX: Destroy invites of anonymized emails (PR #13404)

Anonymizing a user changed their email address, destroyed all associated InvitedUser records, but did not destroy the invites associated to the user.


      expect(Invite.exists?(id: eq(false)

Minor point but I think using .exists? is more intention revealing. Also, it is slightly faster since the ActiveRecord object does not need to be re-hydrated.