Final Patches for RCD related devices. (#74592)

## About The Pull Request
Final closing act for #74527, some more bugs to squash.

1. Fixes broken sprite for rack in RCD UI
![Screenshot
(153)](https://user-images.githubusercontent.com/110812394/230711179-4df6fc5f-6f6c-4680-bb0b-b1caba50152d.png)

2. Fixes #41114 mounted RCD can lay plating on chasm/ any open turf
again

3. Removes unused turf argument inside `try_clean()`, `try_wallmount()`,
& `try_decon()` procs because well it was unused

## Changelog
🆑
refactor: remove unused turf var inside wallmount procs
fix: broken rack sprite inside RCD UI
fix: mounted RCD now lays plating over chasms and open turfs
/🆑

code/modules/asset_cache/assets/rcd.dm

@@ -12,10 +12,10 @@
 		'icons/obj/monitors.dmi' = list("alarm_bitem"),
 		'icons/obj/wallframe.dmi' = list("apc"),
 		'icons/obj/stock_parts.dmi' = list("box_1"),
-		'icons/obj/objects.dmi' = list("bed", "rack"),
+		'icons/obj/objects.dmi' = list("bed"),
 		'icons/obj/smooth_structures/catwalk.dmi' = list("catwalk-0"),
 		'icons/hud/radial.dmi' = list("cnorth", "csouth", "ceast", "cwest", "chair", "secure_windoor", "stool", "wallfloor", "windowsize", "windowtype", "windoor"),
-		'icons/obj/structures.dmi' = list("glass_table", "rwindow0", "reflector_base", "table", "window0"),
+		'icons/obj/structures.dmi' = list("glass_table", "rack", "rwindow0", "reflector_base", "table", "window0"),
 	)
 
 	var/icon/icon