xfs_repair: remove old workqueue stuff in favor of libfrog code

xfs_repair: remove old workqueue stuff in favor of libfrog code

Now that we've made a generic workqueue in libfrog, we can remove the
implementation in xfs_repair and turn the old functions into wrappers
that call do_error if they fail.  There are no functional changes in
this patch, though some of the names and types have changed.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>