m56d ammo for m56 cupola (#6578)

# About the pull request

changes ammo of m56 cupola of a tank to m56d ammo rather then normal
smartgun ammo. it was leftover propably from some super old smartgun
behavior. current ammo was 30 dmg 0 ap with 2 shots per second, for
reference m4ra with iff scope has slightly better firerate with 36 dmg
40 ap with ap ammo and 48 dmg with 5 ap with normal ammo and you can
hold it in hand not have it mounted on a tank. now it has 35 dmg with 50
ap,

# Explain why it's good for the game

with other stats still worse then if you were to move m56d around but it
is not COMPLETE trap anymore, you are still better off leaving the tank
and carring m56d around but at least it can harm the enemy

# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

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screenshots and the `<details>` tags.

</details>


# Changelog
:cl:
balance: m56 cupola uses m56d ammo rather then standard sg ammo
/:cl:

---------

Co-authored-by: vincibrv <[email protected]>
Co-authored-by: harryob <[email protected]>

code/modules/vehicles/hardpoints/hardpoint_ammo/cupola_ammo.dm

@@ -5,7 +5,7 @@
 	icon = 'icons/obj/items/weapons/guns/ammo_by_faction/uscm.dmi'
 	icon_state = "cupola_1"
 	w_class = SIZE_LARGE
-	default_ammo = /datum/ammo/bullet/smartgun
+	default_ammo = /datum/ammo/bullet/machinegun
 	max_rounds = 500
 	gun_type = /obj/item/hardpoint/secondary/m56cupola
 

code/modules/vehicles/hardpoints/secondary/cupola.dm

@@ -28,9 +28,3 @@
 	burst_amount = 3
 	burst_delay = 0.3 SECONDS
 	extra_delay = 0.6 SECONDS
-
-/obj/item/hardpoint/secondary/m56cupola/set_bullet_traits()
-	..()
-	LAZYADD(traits_to_give, list(
-		BULLET_TRAIT_ENTRY(/datum/element/bullet_trait_iff)
-	))