Fixes bubble/hull shield generators not updating air zones, update_nearby_tiles() cleanup.

code/game/objects/structures.dm

@@ -61,6 +61,9 @@
 	if(climbable)
 		verbs += /obj/structure/proc/climb_on
 
+/obj/structure/Del()
+	..()
+
 /obj/structure/proc/climb_on()
 
 	set name = "Climb structure"
@@ -175,4 +178,4 @@
 	if (issilicon(user))
 		user << "<span class='notice'>You need hands for this.</span>"
 		return 0
-	return 1
+	return 1