Drop ordered_mirrorlist code paths

[adrianreber]

@mdomsch described in February that the orderer_mirrorlist code is no longer necessary since Fedora 8. So we could probably drop all occurrences of it.

Fedora versions <= 7 would pick a mirror at random; Fedora > 7 defaulted to
believing the mirror list was ordered. In the MM version table, you find
the ordered_mirrorlist attribute, which is "true" for all versions > 7.

The default_ordered_mirrorlist value told us what to do in the event we
were downloading from a directory not explicitly associated with a version
(e.g. not a repository).

So we can remove the ordered_mirrorlist bits and default to an ordered_mirrorlist