Delete one or more members.
Requires profile_remove_own or profile_remove_any permission for
respectively removing your own account or any account.
Non-admins cannot delete admins.
The function:
- changes author of messages, topics and polls to guest authors.
- removes all log entries concerning the deleted members, except the
error logs, ban logs and moderation logs.
- removes these members' personal messages (only the inbox), avatars,
ban entries, theme settings, moderator positions, poll and votes.
- updates member statistics afterwards.