Adds a modular computer subsystem to shift modPCs away from radios (#71732)

## About The Pull Request

Adds the modular computer subsystem which is meant to replace mod PC's
reliance on networks and radios, specifically the network subsystem, the
ntnet interface, and /datum/ntnet. This PR removes station_root ntnets
entirely, but I tried to keep it small.

This PR also removes a ton of unused vars and defines, such as NTNet
channels that were unused (peer2peer and systemcontrol), atmos networks
(as they were removed a while ago) and NTNet var on relays (its stated
purpose is so admins can see it through varedits, but that's useless now
that it's a subsystem)

I also removed ``setting_disabled`` as a thing the RD can do, it turned
off ALL ntnet systems. However, this was when there were 4 different
ones, now that there's only 2 I thought it was redundant and he could
just click 2 buttons to close them.

## Why It's Good For The Game

``/datum/ntnet``, ``/datum/component/ntnet_interface``, and
``/datum/controller/subsystem/networks`` are all old-code messes that
depend on eachother and is hard for people to understand what exactly it
adds to the game. 90% of its features is allowing the Wirecarp app to
see all the ruins that spawned in-game, which I don't think is something
that we even WANT (why does the RD need to know that oldstation spawned?
Why should they know this anyway??)

This hopefully starts to simplify networks/ntnet to make it easier to
remove in the future, because surely there are better alternatives than
**this**

## Changelog

🆑
refactor: Modular computers NTnet and applications run on its own
subsystem, please report any new bugs you may find.
/🆑

code/modules/modular_computers/file_system/program.dm

@@ -19,7 +19,7 @@
 	var/program_icon_state = null
 	/// Set to 1 for program to require nonstop NTNet connection to run. If NTNet connection is lost program crashes.
 	var/requires_ntnet = FALSE
-	/// Optional, if above is set to 1 checks for specific function of NTNet (currently NTNET_SOFTWAREDOWNLOAD, NTNET_PEERTOPEER, NTNET_SYSTEMCONTROL and NTNET_COMMUNICATION)
+	/// Optional, if above is set to 1 checks for specific function of NTNet (currently NTNET_SOFTWAREDOWNLOAD and NTNET_COMMUNICATION)
 	var/requires_ntnet_feature = 0
 	/// NTNet status, updated every tick by computer running this program. Don't use this for checks if NTNet works, computers do that. Use this for calculations, etc.
 	var/ntnet_status = 1