deleting spamfilter_users should delete linked spamfilter_wblist
When a spamfilter_users entry is removed, it should remove any spamfilter_wblist entries linked to it (where spamfilter_users.id == spamfilter_wblist.rid). This does not happen when the spamfilter_users entry id deleted directly, nor when a mail_user is removed (removing a mail_user does cascade a delete of the corresponding spamfilter_users entry, but not spamfilter_wblist entries tied to those). Note the corresponding spamfilter_wblist_delete events should also be called.