nvme-multipath: remove unused groups_only mode in ana log

groups_only mode in nvme_read_ana_log() is no longer used: remove it.

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anton Eidelman <anton@lightbitslabs.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>