Last min cleanup

What it says in the title

Builds successfully. Hilarious how we had a function that does nothing. +1

Funnily enough, it used to do something back in Doom, when you triggered map effects by crossing lines instead of touching sectors. However, it seems CheckMissileImpact stuck around for a long time even after being made totally useless. =P

merged

mentioned in commit 8b4a64ac