Remove spkac subcommand

Remove spkac subcommand

Google killed efforts to have SPKAC in html5 by zapping it from chrome
a decade ago. This effort doesn't look like it's going anywhere:

https://datatracker.ietf.org/doc/draft-leggett-spkac/

Unfortunately, PHP and Ruby still support NETSCAPE_SPKI, so we can't
kill that code, but I see no real reason we need to support this in our
openssl command. If the need should arise we can write a somewhat less
poor version of this.

ok jsing