Dont audit-log message deletions against bots

[Zabuzard]

Overview

Our mod_audit_log channel often contains message deletions against our bot, such as:

There is nothing wrong with this per-se, but it generates unecessary noise and the point of the channel is to be noise-free.

So I am suggesting that the audit-logger routine should simply skip message deletions against bots. (there is always discords own audit log if a true full history of all actions has to be checked).

Other actions against bots should be kept, such as bans.