Disable damagetext in instagib

I want to make it clear that Overkill is not Insta and although this is not much maybe some players will notice that our Nex does 100 damage as opposed to Vaporizer which just kills instantly.

Ideally there would be a defaultInstagib.cfg file that disables damagetext but that would require server admins to actually start using it instead of just g_instagib 1 which would mean that we have to intentionally break g_instagib 1 so they notice. That would probably not get accepted (as quickly).