Proximity sensing refactor (#425)

code/game/turfs/turf.dm

@@ -13,8 +13,6 @@
 
 	flags = CAN_BE_DIRTY
 
-	var/list/proximity_checkers
-
 	var/image/obscured	//camerachunks
 
 	var/list/image/blueprint_data //for the station blueprints, images of objects eg: pipes
@@ -156,10 +154,6 @@
 	return 1 //Nothing found to block so return success!
 
 /turf/Entered(atom/movable/AM)
-	for(var/A in proximity_checkers)
-		var/atom/B = A
-		B.HasProximity(AM)
-
 	if(explosion_level && AM.ex_check(explosion_id))
 		AM.ex_act(explosion_level)