tor-hsservice: Remove dead code from the descriptor publisher

This MR removes a leftover #![allow(dead_code, unused_variables)] in the descriptor publisher that was suppressing a bunch of dead code warnings.

Most of the warnings were straightforward to fix.

gabi-250/arti@34d2378b removes a significant chunk of unused code that has to do with encrypting the second layer of descriptor with the keys of the authorized clients. I will be reimplementing all of it as part of #1292 (closed).