Since commit 0653c358 ("scsi: Drop gdth driver"), functions
scsi_{get,free}_host_dev() no longer have any in-tree users, so delete
them.

Link: https://lore.kernel.org/r/1631528047-30150-1-git-send-email-john.garry@huawei.comReviewed-by: NBart Van Assche <bvanassche@acm.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>
Nacked-by: NHannes Reinecke <hare@suse.de>