Remove limitation of mentions/pings in forums

I see that forums have a similar ping limitation as threads where a role can't have more than 100 people on it in order to ping them.

I run a server where members can assign roles to themselves related to the skills they possess so others can ping them with job opportunities (@artist, @writer, etc.). This doesn't work when each of the roles have 300+ members attached to it and doing this in a regular text thread can get really messy.