dm vdo: remove all sysfs interfaces

Also update target major version number.

All info is (or will be) accessible through alternative interfaces
(e.g. "dmsetup message", module params, etc).

Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Ken Raeburn <raeburn@redhat.com>
Signed-off-by: Matthew Sakai <msakai@redhat.com>