Hides worn PDAs (#74838)

## About The Pull Request

PDAs no longer have a visible appearance on your character when equipped
in the belt or ID slot.


![image](https://user-images.githubusercontent.com/7483112/232916683-02e41ece-6c70-4cac-b242-24fb60b6c41a.png)

![image](https://user-images.githubusercontent.com/7483112/232916703-40d0fc65-ed25-4a7b-97be-e09c5925ba44.png)

Pictured:

![image](https://user-images.githubusercontent.com/7483112/232915339-ae3b9879-9415-476f-ba89-a7e59bd6a749.png)
Me uh... not visibly wearing a PDA?

## Why It's Good For The Game

There's virtually no game advantage gained by knowing whether someone is
or is not wearing a PDA, and even if there were they could just as
easily have it in a pocket or other storage slot.
They create visual noise on your sprite and are an accessory that
virtually everyone always has, making the game look worse.
When ID card sprites were restored as part of a bug fix when introducing
missing worn icon unit testing, they were intentionally hidden again for
similar reasons.

## Changelog

🆑
imagedel: you can no longer tell if someone is wearing a PDA by looking
at them
/🆑

code/modules/modular_computers/computers/item/pda.dm

@@ -2,7 +2,7 @@
 	name = "pda"
 	icon = 'icons/obj/modular_pda.dmi'
 	icon_state = "pda"
-	worn_icon_state = "pda"
+	worn_icon_state = "nothing"
 	base_icon_state = "tablet"
 	greyscale_config = /datum/greyscale_config/tablet
 	greyscale_colors = "#999875#a92323"