Renames vars on pdas and removes ntnet_relays glob (#79595)

## About The Pull Request

- replaces the ntnet_relays global list with ``get_machines_by_type``
- renames ``transfer_access`` var on PDA to ``download_access`` &
``required_access`` to ``run_access`` to better describe what they do,
because on more than one ocassion I've confused myself with the two
terms and ended up doing something unintentional (see:
https://github.com/tgstation/tgstation/pull/74269)

## Why It's Good For The Game

Kills a useless global list and makes pda code a little less confusing.

## Changelog

Nothing player-facing.

code/modules/modular_computers/file_system/programs/ntdownloader.dm

@@ -143,7 +143,7 @@
 			"installed" = !!computer.find_file_by_name(programs.filename),
 			"compatible" = check_compatibility(programs),
 			"size" = programs.size,
-			"access" = programs.can_run(user, transfer = TRUE, access = access),
+			"access" = programs.can_run(user, downloading = TRUE, access = access),
 			"verifiedsource" = programs.available_on_ntnet,
 		))