Replace explicit z-level checks with defines

code/modules/power/apc.dm

@@ -941,7 +941,7 @@
 	if(!malf.can_shunt)
 		to_chat(malf, "<span class='warning'>You cannot shunt!</span>")
 		return
-	if(!(src.z in GLOB.station_z_levels))
+	if(!is_station_level(z))
 		return
 	occupier = new /mob/living/silicon/ai(src, malf.laws, malf) //DEAR GOD WHY?	//IKR????
 	occupier.adjustOxyLoss(malf.getOxyLoss())

code/modules/power/singularity/narsie.dm

@@ -61,7 +61,7 @@
 			var/mob/living/L = cult_mind.current
 			L.narsie_act()
 	for(var/mob/living/player in GLOB.player_list)
-		if(player.stat != DEAD && (player.loc.z in GLOB.station_z_levels) && !iscultist(player))
+		if(player.stat != DEAD && is_station_level(player.loc.z) && !iscultist(player))
 			souls_needed[player] = TRUE
 	soul_goal = round(1 + LAZYLEN(souls_needed) * 0.6)
 	INVOKE_ASYNC(src, .proc/begin_the_end)