scsi: mvsas: remove unused symbol 'mvs_th'

This symbol has no users so remove it.

Link: https://lore.kernel.org/r/20200415085053.7633-1-yanaijie@huawei.com


Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>