Kill processing_objects (#3398)

code/game/objects/items/weapons/material/ashtray.dm

@@ -52,7 +52,7 @@
 			var/obj/item/clothing/mask/smokable/cigarette/cig = W
 			if (cig.lit == 1)
 				src.visible_message("[user] crushes [cig] in \the [src], putting it out.")
-				processing_objects.Remove(cig)
+				STOP_PROCESSING(SSprocessing, cig)
 				var/obj/item/butt = new cig.type_butt(src)
 				cig.transfer_fingerprints_to(butt)
 				qdel(cig)

code/game/objects/items/weapons/material/material_weapons.dm

@@ -57,11 +57,11 @@
 		if(applies_material_colour)
 			color = material.icon_colour
 		if(material.products_need_process())
-			processing_objects |= src
+			START_PROCESSING(SSprocessing, src)
 		update_force()
 
 /obj/item/weapon/material/Destroy()
-	processing_objects -= src
+	STOP_PROCESSING(SSprocessing, src)
 	return ..()
 
 /obj/item/weapon/material/apply_hit_effect()