hs-v2: Farewell Old Friend

The 0.4.6 merge window has opened earlier this year, thus it is time to say goodbye to our great friend, the onion service version 2.

It has served us incredibly well, it has done its time and can now retire with pride and glory.

This ticket is about the removal of v2 support from tor.git. As per our deprecation timeline: https://lists.torproject.org/pipermail/tor-dev/2020-June/014365.html