[MIRROR] Adds a modular computer subsystem to shift modPCs away from radios [MDB IGNORE] (#17942)

* 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.
/🆑

* Adds a modular computer subsystem to shift modPCs away from radios

* Fixed contractor uplink

Co-authored-by: John Willard <53777086+JohnFulpWillard@users.noreply.github.com>
Co-authored-by: tastyfish <crazychris32@gmail.com>

code/modules/modular_computers/NTNet/NTNRC/conversation.dm

@@ -34,13 +34,11 @@
 	if(id > MAX_CHANNELS)
 		qdel(src)
 		return
-	if(SSnetworks.station_network)
-		SSnetworks.station_network.chat_channels.Add(src)
+	SSmodular_computers.chat_channels.Add(src)
 	return ..()
 
 /datum/ntnet_conversation/Destroy()
-	if(SSnetworks.station_network)
-		SSnetworks.station_network.chat_channels.Remove(src)
+	SSmodular_computers.chat_channels.Remove(src)
 	for(var/datum/computer_file/program/chatclient/chatterbox as anything in (active_clients | offline_clients))
 		purge_client(chatterbox)
 	return ..()