Fixes a duplicate sprite error primarily on firearms. (#6005)

## About The Pull Request

Some guns (Probably other items too) have been seeing double for a while
now and this isn't just because you're an alcoholic. With certain guns,
a Miecz, a Lanca, a Renoster, a Kiboko, the VARS launcher, and the hand
slot shows you two sprites offset by about eight pixels, OK actually 8
pixels exactly because that's what the code told it to do. Hold a
disabler or a WT-550 and everything is perfectly fine. That was the
clue.

Every affected gun suffering from this defect drew from an "oversized"
sprite sheet. `guns_48.dmi` is 48 pixels wide instead of 32, and a
sprite that wide had to carry a negative `base_pixel_x` to sit centered
on its tile. Every gun that was fine is a plain 32 by 32 vanilla one
sitting at zero. TG doesn't have as many ginormous guns (actually, there
are probably a few, but I didn't test every possible gun, that would
take too long)

**The reason that this matters**: your held item is drawn twice behind
the scenes `/mob/living/carbon/human/get_held_overlays()` shoves the
item onto your client's screen with a `screen_loc`, which is how hand
slots used to work. Hand slots don't work that way any more; someone
rewrote inventory slots which now draw the item through the slot's
`vis_contents` instead, and upstream deleted their copy of this line at
the time. As a downstream, Bubber did not.

So both paths have been drawing your item this whole time. Anything
sitting at pixel offset zero lands in exactly the same spot twice is
invisible. Anything wider than a tile is shifted 8 pixels over, the two
copies separate, and you get a freakish mutant ghost gun.

This deletes the one line that pushes the item onto your own screen. The
observer push underneath it stays so it doesn't break observing people.

One line fix, a whole afternoon of fucking around to get there. 

## Why It's Good For The Game

Guns stop being haunted. The possibility of adding intentionally haunted
guns at a later date yet remains.

More usefully, this could theoretically afflict any item with a sprite
bigger than one tile, not just guns. Guns are simply the most common
"oversized sprite" incidence, so that's where it showed up.

## Testing

Tested a wide array of items and weapons to make sure the fix works and
didn't have any unforeseen negative consequences. Swapped hands, dropped
and picked back up, took the item and put it on my vest and took it back
out, checked items still stay in the inventory slot properly every time.
Ghosted and observed a player holding a gun, still renders correctly.

I will note that some sprites still sit very slightly left of centr
inside the box, because they keep the offset that centres them on a
tile. That's cosmetic and I think it was there before; if anyone
actually turns out to care that is a separate issue that will require a
separate fix.

## Changelog

🆑
fix: Certain items no longer render a doubled ghost copy in your hand
slot.
/🆑

code/modules/mob/living/carbon/human/human_update_icons.dm

@@ -663,7 +663,10 @@ There are several things that need to be remembered:
 		var/held_index = get_held_index_of_item(worn_item)
 		if(client && hud_used && hud_used.hud_version != HUD_STYLE_NOHUD)
 			worn_item.screen_loc = ui_hand_position(held_index)
-			client.screen += worn_item
+			// BUBBER EDIT REMOVAL BEGIN - pushing the held item onto our own client's screen here is how
+			// hand slots worked before the inventory slot rewrite. This alternate behavior is needed to stop duplicate item sprites appearing inhand.
+			// ORIGINAL: client.screen += worn_item
+			// BUBBER EDIT REMOVAL END
 			if(observers?.len)
 				for(var/M in observers)
 					var/mob/dead/observe = M