Remove pkinit_win2k_require_binding; always require RFC 4556 ReplyKeyPack

This pull request is less of a no-brainer than the other recent PKINIT pull requests.  It removes the ability to interoperate against unpatched Server 2003 PKINIT in exchange for better security.  Accepting a draft9 ReplyKeyPack means allowing the KDC reply to not be properly bound to the request.

The "Remove PKINIT longhorn compatibility option" commit is pull request #148; ignore it.  This commit touches some of the same code, so rather than create future merge conflicts, I based this branch on the longhorn removal branch.