With the availablility of a sysfs device attribute for examining disk serial
numbers the ioctl is no longer needed.  The user-space changes for this aren't
upstream yet so we don't have any users to worry about.
Signed-off-by: NRyan Harper <ryanh@us.ibm.com>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>