Gives Traitor AIs the Syndicate Channel!

This PR is intended to support #5283 .
- Traitor AIs, when set as a traitor, will be given a new internal radio
calibrated to hear and transmit to the encrypted syndicate frequency.

Since traitors can buy a headset key for getting the Syndicate Channel,
Traitor AIs can get one too, as they cannot purchase their own TC items.
Moved some things around!

All radios now have a keyslot var (replacing keyslot1 for headsets).
- recalculateChannels() proc moved to radios instead of just headsets.
- Removed the duplicated recalc proc for borg radios.
- Moved the translate vars to radios as well.
- The syndicate headset subtype has been removed in favor of using the
make_syndie() proc on it instead.
Merge remote-tracking branch 'remotes/upstream/master' into Potato_AI_Wants_To_Hear_You_Scream_Too

Conflicts:
	code/modules/mob/living/silicon/ai/ai.dm
Merge pull request #5654 from GunHog/Potato_AI_Wants_To_Hear_You_Scream_Too

Gives Traitor AIs the Syndicate Channel!