Automatically remove non bot command messages from #bot-spam

[AniLeo]

There are some non bot messages sent in the middle of the channel. Due to all the bot spam, it's not feasible to check it all the time.

As such, we should not allow regular chatting in that channel at all. All messages that are not RPCS3 Bot commands should automatically be removed, and optionally, the user should be informed that they cannot chat in that channel.