Remove the AuthDirRejectUnlisted config option

This is in preparation for a big patch series removing the entire Naming
system from Tor. In its wake, the approved-routers file is being
deprecated, and a replacement option to allow only pre-approved routers
is not being implemented.
Fix add_fingerprint_to_dir() doc and signature

This function never returns non-null, but its usage doesn't reflect
that. Let's make it explicit. This will be mostly overridden by later
commits, so no changes file here.
Remove support for naming directory authorities

This implements the meat of #12899. This commit should simply remove the
parts of Tor dirauths used to check whether a relay was supposed to be
named or not, it doesn't yet convert to a new mechanism for
reject/invalid/baddir/badexiting relays.
Merge branch 'bug12899_squashed'
Remove dirauth support for the BadDirectory flag

Implements the first half of #13060. The second half will be to remove
client support, too.
Remove client-side bad directory logic

Implements the second half of #13060.