makes w_class use defines (#9848)

code/modules/multiz/mobile_ladders.dm

@@ -7,7 +7,7 @@
 	contained_sprite = TRUE
 	throw_range = 3
 	force = 10
-	w_class = 4.0
+	w_class = ITEMSIZE_LARGE
 	slot_flags = SLOT_BACK
 
 /obj/item/ladder_mobile/proc/place_ladder(atom/A, mob/user)
@@ -105,4 +105,4 @@
 		qdel(src)
 	else
 		QDEL_NULL(target_up)
-		qdel(src)
+		qdel(src)