xfs_scrub_all.cron: move to package data directory

xfs_scrub_all.cron: move to package data directory

cron jobs don't belong in /usr/lib.  Since the cron job is also
secondary to the systemd timer, it's really only provided as a courtesy
for distributions that don't use systemd.  Move it to @datadir@, aka
/usr/share/xfsprogs.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Neal Gompa <neal@gompa.dev>
Reviewed-by: Christoph Hellwig <hch@lst.de>