libafsauthent: Remove obsolete HP-UX workaround

libafsauthent: Remove obsolete HP-UX workaround

This workaround is no longer relevant. It is also error-prone and
there are far better ways to achieve a similar result, so get rid of
it.

Change-Id: If77f0cd95c8c608913d0c8717729a05c1ad67df9
Reviewed-on: http://gerrit.openafs.org/5811
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>