!mjolnir kick *: Don't remove the bot itself

Removing all users via `!mjolnir kick *` can be useful for closing a channel. However, mjolnir will remove itself before having removed all other users and globs are not sophisticated enough to avoid this.

I would suggest that `!mjolnir kick` should never remove the bot itself.

Start by locating the implementation of the `!mjolnir kick` command and its `*` glob handling. Verify that a kick-all operation skips the bot while still removing other users, and test the command behavior with a channel containing multiple users.

Written by the indexing model from the issue text.