'uds_attribute' is unused since
commit a9da0fb6 ("dm vdo: remove all sysfs interfaces").

Remove it.
Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>