[SCSI] fix callers of scsi_remove_device() who already hold the scan muted

This patch (as544) adds a private entry point to scsi_remove_device, for
use when callers already own the scan_mutex.  The appropriate callers are
modified to use the new entry point.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>