Remove mouse_opacity 2 from all hostile mobs except hivelords

Created by: dylanstrategie

That was a band-aid fix to a problem that didn't exist (not being able to hit hostile mobs despite all of them being the size of a normal mob, maybe save for baby carps)

I kept the mouse_opacity for hivelords since those things are fucking impossible to nail otherwise

This should also make things less painful for player-controlled simple mobs

Fixes #6127 (closed)