Minimize draft9 PKINIT code by removing dead code

Minimize draft9 PKINIT code by removing dead code

The PKINIT client code doesn't use decode_krb5_pa_pk_as_rep_draft9,
which is fortunate because it doesn't work (see issue #7072).
Instead, it passes both kinds of PKINIT replies through
decode_krb5_pa_pk_as_rep, then decodes the un-enveloped CMS data in
alternative 1 (encKeyPack) as either an RFC or draft9 ReplyKeyPack.
So, remove the unused broken pa_pk_as_rep_draft9 decoder.

For pa_pk_as_req_draft9, we only use two of the fields on encode and
only one of those on decode.  So, get rid of the unused fields and
the krb5_trusted_ca structure, and reduce the encoder and decoder
sequences to the minimum necessary fields.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@25689 dc483132-0cff-0310-8789-dd5450dbe970