Windows: Build libafsauthent.dll against mtafsubik.lib

Instead of building a private copy of the ubik objects, link
against mtafsubik.lib.

Change-Id: Ic72e0ea963ddb870d082f7a3746f978ba785bbbc
Reviewed-on: http://gerrit.openafs.org/9302
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>