lightnvm: remove unused attrs in nvm_id structs

The nvm_id, nvm_id_group and nvm_addr_format data structures contain
reserved attributes. They are unused by media managers and targets.
Remove them.

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