misc: remove the dangerous_scrub group

misc: remove the dangerous_scrub group

Now that online fsck has been in the upstream kernel for 8 months, I
think it's stabilized enough that the scrub functionality tests don't
need to hide behind the "dangerous" label anymore.  Move them all to the
scrub group and delete the dangerous_scrub group.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Zorro Lang <zlang@kernel.org>