CORSAT poddoor and LZ fixes (#5029)

# About the pull request

Fixes CORSAT's LZs so that they can be landed on using the modern
shuttle system.

Removed the icon from poddoors supposedly invisible `filler_object` so
they will actually be invisible, as intended. There's a lot more to be
said about wide poddoors using a completely separate system from wide
airlocks but -- well, I don't want to.

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# Explain why it's good for the game

A little less friction using an unmaintained map like CORSAT.
# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Before, LZs

![image](https://github.com/PvE-CMSS13/PvE-CMSS13/assets/14267245/6a92c821-2507-4bf4-8e69-d994dce16925)
Before, closed poddoors

![image](https://github.com/PvE-CMSS13/PvE-CMSS13/assets/14267245/9cc0ff68-efef-4d05-a1ba-b3c7c8ae86df)
Before, open poddoors

![image](https://github.com/PvE-CMSS13/PvE-CMSS13/assets/14267245/8b89866e-7b2d-499e-8b7c-858a8df2e3e3)

After, LZs

![image](https://github.com/PvE-CMSS13/PvE-CMSS13/assets/14267245/20348a33-e36d-4588-a9d0-06fa8bf61ea6)
After, closed poddoors

![image](https://github.com/PvE-CMSS13/PvE-CMSS13/assets/14267245/e63c0624-0e77-409c-af4a-c2290292517a)
After, open poddoors

![image](https://github.com/PvE-CMSS13/PvE-CMSS13/assets/14267245/62aacf64-2e00-445d-bfd5-a414121e84aa)

</details>


# Changelog
:cl:
fix: CORSAT poddoors no longer have extra sprites overlaid on them
maptweak: CORSAT LZs can be used by shuttles
/:cl:

code/game/machinery/doors/poddoor.dm

@@ -240,6 +240,7 @@
 
 /obj/structure/machinery/door/poddoor/filler_object
 	name = ""
+	icon = null
 	icon_state = ""
 	unslashable = TRUE
 	unacidable = TRUE

maps/map_files/CORSAT/Corsat.dmm

@@ -37445,7 +37445,6 @@
 /area/corsat/gamma/biodome/virology)
 "drp" = (
 /obj/docking_port/stationary/marine_dropship/lz1{
-	dwidth = 1;
 	name = "Gamma Landing Zone"
 	},
 /turf/open/floor/plating,
@@ -38223,7 +38222,6 @@
 /area/corsat/omega/complex)
 "dUj" = (
 /obj/docking_port/stationary/marine_dropship/lz2{
-	dwidth = 1;
 	name = "Sigma Landing Zone"
 	},
 /turf/open/floor/plating,