removes did_fire variable (#3415)

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## About The Pull Request
removes did_fire variable that does nothing but throw an error
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## Why It's Good For The Game
mildly annoying
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## Changelog

:cl:
del: unused did_fire var
/:cl:

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code/modules/projectiles/gun.dm

@@ -984,7 +984,6 @@
 		human_holder = src
 	for(var/obj/item/gun/at_risk in get_all_contents())
 		var/chance_to_fire = GUN_NO_SAFETY_MALFUNCTION_CHANCE_MEDIUM
-		var/did_fire = FALSE
 		if(human_holder)
 			// gun is less likely to go off in a holster
 			if(at_risk == human_holder.s_store)