According to OONI stunreachability measurements, stun://stun.altar.com.pl:3478 has been showing 100% anomalies since 2022-10-13. If it's down for good, we ought to remove it from the list of STUN servers.

https://explorer.ooni.org/chart/mat?test_name=stunreachability&since=202...

Previous mention of stun.altar.com.pl:

https://lists.torproject.org/pipermail/anti-censorship-team/2022-May/000237....