nvmet: remove old function prototype

nvmet_subsys_nsid_exists() doesn't exist anymore

Fixes: 74d1696 ("nvmet-loop: avoid using mutex in IO hotpath")
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/target/nvmet.h

@@ -647,7 +647,6 @@ void nvmet_subsys_disc_changed(struct nvmet_subsys *subsys,
 		struct nvmet_host *host);
 void nvmet_add_async_event(struct nvmet_ctrl *ctrl, u8 event_type,
 		u8 event_info, u8 log_page);
-bool nvmet_subsys_nsid_exists(struct nvmet_subsys *subsys, u32 nsid);
 
 #define NVMET_MIN_QUEUE_SIZE	16
 #define NVMET_MAX_QUEUE_SIZE	1024