(Partially) unify XDR for libuafs and libafs

The libuafs build was getting xdr_vector() from both afsaux.c and
xdr_update.c, but because of the rules for creating static libraries,
this did not cause build errors.

The libafs build is sensitive to duplicate symbols, and was only
getting xdr_vector() from afsaux.c; libafs was not building xdr_update.c
or xdr_refernce.c (that is not a typo).

Remove duplicate xdr_vector() from afsaux.c, and build xdr_update.c
and xdr_refernce.c into libafs.

Remove the unused #define of AUTH_DES.

Change-Id: I58ea595d424801697acb07406664ede33aeaf026
Reviewed-on: http://gerrit.openafs.org/11545
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: D Brashear <shadow@your-file-system.com>