drbd: drop API_VERSION define

Use the genetlink api version as defined in drbd_genl_api.h.

Signed-off-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Reviewed-by: Joel Colledge <joel.colledge@linbit.com>
Link: https://lore.kernel.org/r/20230113123506.144082-3-christoph.boehmwalder@linbit.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>