lightnvm: remove sysfs configuration interface

LightNVM used to be managed and configured through sysfs. Since the
introduction of management ioctls this interface is redundant and
outdated. Get rid of it.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>