Revert "Stairs are Dangerous" (#19484)

Unfortunately most of the map is kind of unplayable or not mapped in
mind with stairs being untraversable for roller beds or wheelchairs.
Remapping every map to work with this mechanic is also not something I
am interested in.

---------

Co-authored-by: Matt Atlas <liermattia@gmail.com>

code/modules/multiz/structures.dm

@@ -284,11 +284,6 @@
 				playsound(src, 'sound/effects/stairs_step.ogg', 50)
 				playsound(target, 'sound/effects/stairs_step.ogg', 50)
 
-/obj/structure/stairs/Crossed(obj/O)
-	if(istype(O))
-		O.stair_act()
-	return ..()
-
 /obj/structure/stairs/proc/upperStep(var/turf/T)
 	return (T == loc)
 
@@ -386,11 +381,6 @@
 	icon = 'icons/obj/structure/stairs.dmi'
 	icon_state = "np_stair"
 
-/obj/structure/platform_stairs/Crossed(obj/O)
-	if(istype(O))
-		O.stair_act()
-	return ..()
-
 /obj/structure/platform_stairs/south_north_solo
 	icon_state = "p_stair_sn_solo_cap"