Refactor out an old cooldown system (#22179)

You can do this a lot more efficiently with world time cooldowns,
avoiding the need for spawn counters

code/modules/assembly/timer.dm

@@ -42,15 +42,12 @@
 
 
 /obj/item/device/assembly/timer/proc/timer_end()
-	if((!secured)||(cooldown > 0))
-		return 0
+	if(!secured || next_activate > world.time)
+		return FALSE
 	pulse(0)
 	audible_message("\icon[src] *beep* *beep*", null, 3)
-	cooldown = 2
-	spawn(10)
-		process_cooldown()
-		if(loop)
-			timing = 1
+	if(loop)
+		timing = 1
 	update_icon()