delete tor-assistants list

There is still a tor-assistants list: https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-assistants
but it has a strange group of past people on it, and I don't see anybody successfully using it, except Micah using it in Nov 2019 and Jan 2020 in response to nextcloud password resets, and I have no idea how that happened but it doesn't seem mission-critical. :)

Long ago we used tor-assistants@tpo (not @lists.tpo) for people to help me answer questions from the outside world, but we long ago stopped successfully doing that, and somebody made a mailman list out of it but it never really got off the ground. Now there is tor-team@lists.tpo for a similar but different role.

In any case, this list is not in use, and nobody has been maintaining its subscriber list. It's a good time to clean it up.

Thanks!