Replaces GoonPS scheduled_tasks and obj processing with SMC processing subsystems and timer

code/modules/shieldgen/directional_shield.dm

@@ -102,14 +102,14 @@
 	var/low_color = "#FF0000"			// Color the shield will drift towards as health is lowered.  Deep red.
 
 /obj/item/shield_projector/New()
-	processing_objects += src
+	START_PROCESSING(SSobj, src)
 	if(always_on)
 		create_shields()
 	..()
 
 /obj/item/shield_projector/Destroy()
 	destroy_shields()
-	processing_objects -= src
+	STOP_PROCESSING(SSobj, src)
 	return ..()
 
 /obj/item/shield_projector/proc/create_shield(var/newloc, var/new_dir)

code/modules/shieldgen/handheld_defuser.dm

@@ -16,7 +16,7 @@
 	qdel(cell)
 	cell = null
 	if(enabled)
-		processing_objects.Remove(src)
+		STOP_PROCESSING(SSobj, src)
 	. = ..()
 
 /obj/item/weapon/shield_diffuser/get_cell()
@@ -42,9 +42,9 @@
 	enabled = !enabled
 	update_icon()
 	if(enabled)
-		processing_objects.Add(src)
+		START_PROCESSING(SSobj, src)
 	else
-		processing_objects.Remove(src)
+		STOP_PROCESSING(SSobj, src)
 	to_chat(usr, "You turn \the [src] [enabled ? "on" : "off"].")
 
 /obj/item/weapon/shield_diffuser/examine()

code/modules/shieldgen/shield_gen.dm

@@ -42,7 +42,7 @@
 	return ..()
 
 /obj/machinery/shield_gen/Destroy()
-	QDEL_NULL_LIST(field)
+	QDEL_LIST_NULL(field)
 	return ..()
 
 /obj/machinery/shield_gen/emag_act(var/remaining_charges, var/mob/user)