Atmospheric computer circuit additions.

Adds several missing variables used in the construction and deconstruction set of gas management computers. Fixes #11392.
Computers also no longer attemps to qdel a type on Destroy()

code/game/machinery/computer/computer.dm

@@ -12,11 +12,6 @@
 	var/light_range_on = 3
 	var/light_power_on = 1
 
-/obj/machinery/computer/Destroy()
-	qdel(circuit)
-	circuit = null
-	return ..()
-
 /obj/machinery/computer/initialize()
 	power_change()