[krbdev.mit.edu #7072] PKINIT pk_as_rep_draft9 encoding issues

[Greg Hudson via RT]

It turns out we don't use decode_krb5_pa_pk_as_rep_draft9 anywhere in the 
PKINIT plugin.

Instead, we pass both kinds of PKINIT replies through 
decode_krb5_pa_pk_as_rep, which should succeed for the encKeyPack 
alternative and fail for the Diffie-Hellman alternative.  For the 
encKeyPack alternative, the unwrapped envelope data is then decoded as 
either an RFC or draft9 ReplyKeyPack.

So the broken pa_pk_as_rep_draft9 decoder can be removed.