tor-proto/tor-circmgr: remove "ntor_v3" feature flag (and always enable)
My understanding is that ntor v3 can be always-enabled now, and we'll need this for congestion control, so I've removed the "ntor_v3" feature from tor-proto and tor-cirgmr. It seems best to do this right after a new release so that this has more time to sit as stable behaviour before the next release.
Note: Don't merge until after the release when the main branch is unfrozen. Edit: Marking as "draft" just to prevent merges.
Edited by opara