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.
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.