Shield impact optimization (#8635)

* Test 2: Ubuntu Update Required

* Revert Test 2: Ubuntu Update Required

* shield effects now use timer system for self qdeletion

* better

Author: vode-code

code/modules/shield_generators/shield.dm

@@ -13,9 +13,7 @@
 	density = FALSE
 
 /obj/effect/shield_impact/New()
-	spawn(2 SECONDS)
-		qdel(src)
-
+	QDEL_IN(src, 2 SECONDS)
 
 /obj/effect/shield
 	name = "energy shield"