Remove tor-moderators list

There's a tor-moderators list: https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-moderators which is completely unused -- no messages ever sent, and nobody ever subscribed. Apparently we made it in legacy/trac#32155 (moved).

Let's delete it, so people don't look at it and think there's a sekrit list where people are conspiring.

(Moderators for various Tor services and forums do talk to each other, but clearly they have developed other ways of doing it rather than using this list.)

Thanks!