Removes unused pressure_resistance variable.

This is used with FEA not ZAS

Though it's kind of funny to look at what some of these values were set at.
(For reference: ONE_ATMOSPHERE = 101.325)

code/game/objects/structures/window_spawner.dm

@@ -9,7 +9,6 @@
 	icon_state = "wingrille"
 	density = 1
 	anchored = 1.0
-	pressure_resistance = 4*ONE_ATMOSPHERE
 	var/win_path = /obj/structure/window/basic
 	var/activated