Converts Most Destroys to use QDEL_NULL

code/modules/power/apc.dm

@@ -178,11 +178,8 @@
 	area.power_change()
 	if(occupier)
 		malfvacate(1)
-	qdel(wires)
-	wires = null
-	if(cell)
-		qdel(cell) // qdel
-		cell = null
+	QDEL_NULL(wires)
+	QDEL_NULL(cell)
 	if(terminal)
 		disconnect_terminal()
 	area.apc -= src

code/modules/power/gravitygenerator.dm

@@ -52,8 +52,7 @@ var/const/GRAV_NEEDS_WRENCH = 3
 
 /obj/machinery/gravity_generator/part/Destroy()
 	set_broken()
-	if(main_part)
-		qdel(main_part)
+	QDEL_NULL(main_part)
 	return ..()
 
 //

code/modules/power/singularity/particle_accelerator/particle_control.dm

@@ -30,8 +30,7 @@
 /obj/machinery/particle_accelerator/control_box/Destroy()
 	if(active)
 		toggle_power()
-	qdel(wires)
-	wires = null
+	QDEL_NULL(wires)
 	return ..()
 
 /obj/machinery/particle_accelerator/control_box/attack_ghost(user as mob)

code/modules/power/supermatter/supermatter.dm

@@ -72,9 +72,7 @@
 
 /obj/machinery/power/supermatter_shard/Destroy()
 	investigate_log("has been destroyed.", "supermatter")
-	if(radio)
-		qdel(radio)
-		radio = null
+	QDEL_NULL(radio)
 	poi_list.Remove(src)
 	return ..()