Remove pkinit_win2k_require_binding option

When constructing a draft9 PKINIT request, always include
KRB5_PADATA_AS_CHECKSUM padata to ask for an RFC 4556 ReplyKeyPack.
Do not accept a draft9 ReplyKeyPack in the KDC response.

For now, retain the krb5_reply_key_pack_draft9 ASN.1 codec and the KDC
support for generating a draft9 ReplyKeyPack when a draft9 PKINIT
request does not contain KRB5_PADATA_AS_CHECKSUM.

ticket: 7933