[SCSI] Revert "[SCSI] fix async probe regression"

This reverts commit 43a8d39d.

Commit 43a8d39d fixed the fact that wait_for_device_probe() was unable
to flush sd probe work.  Now that sd probe work is once again flushable
via wait_for_device_probe() this workaround is no longer needed.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Eldad Zack <eldad@fogrefinery.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>