Add variables for shadow form/invis hatred calculations, raise hatred removed by those spells.

Increase the hatred removed by invis from 50 to 85, and that removed by shadow form from 25 to 60 to counter increased hatred added by vision. These will allow a player to get closer to (but not on top of) a monster without triggering aggro, dependent on how well that monster can see (how high its vision distance is, which also acts as a proxy for how acute its eyesight is).

Removed two unused variables from brain.kod (old distance variables).