nvme: rename nvme_mpath_shutdown_disk to nvme_mpath_remove_disk

In the NVMe context, the term "shutdown" has a specific technical
meaning. To avoid confusion, this commit renames the nvme_mpath_
shutdown_disk function to nvme_mpath_remove_disk to better reflect
its purpose (i.e. removing the disk from the system). However,
nvme_mpath_remove_disk was already in use, and its functionality
is related to releasing or putting the head node disk. To resolve
this naming conflict and improve clarity, the existing nvme_mpath_
remove_disk function is also renamed to nvme_mpath_put_disk.

This renaming improves code readability and better aligns function
names with their actual roles.

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>