Remove options for configuring HS authorities.

(There is no longer meaningfully any such thing as a HS authority,
since we stopped uploading or downloading v0 hs descriptors in
0.2.2.1-alpha.)

Implements #10881, and part of #10841.
Tweak DirAuthority documentation

Per a comment from karsten, there is no longer v2 authority support,
so stop pretending there is. Also, fix a grammar error.x
Merge branch 'bug10881'