Remove the Tor v2 HS from the Chat kb page. (#453)

Remove the Tor v2 HS from the Chat kb page. (#453)

Version 2 hidden services are on a deprecation path that starts from September and finalises late 2021.
We should probably remove the old .onion from the help docs.

The deprecation to obsolescence timeline from their mailing list:

  1) September 15th, 2020
     0.4.4.x: Tor will start warning onion service operators and clients that
              v2 is deprecated and will be obsolete in version 0.4.6

  2) July 15th, 2021
     0.4.6.x: Tor will no longer support v2 and will be removed from the code
              base.

  3) October 15th, 2021
     We will release new stable versions for all supported series that will
     disable v2.

https://lists.torproject.org/pipermail/tor-dev/2020-June/014365.html