Turn more unmanaged global vars into GLOB (#20446)

Turned a ton of unmanaged globals into managed globals.
Refactored some UT output.
Removed some unused things, including vars.
Added a test to ensure people don't keep adding new unmanaged vars.

code/modules/modular_computers/file_system/computer_file.dm

@@ -1,4 +1,4 @@
-var/global/file_uid = 0
+GLOBAL_VAR_INIT(file_uid, 0)
 
 /datum/computer_file
 	var/filename = "NewFile"								// Placehard_drive. No spacebars
@@ -13,8 +13,8 @@ var/global/file_uid = 0
 
 /datum/computer_file/New()
 	..()
-	uid = file_uid
-	file_uid++
+	uid = GLOB.file_uid
+	GLOB.file_uid++
 
 /datum/computer_file/Destroy()
 	if(!hard_drive)