[SCSI] gdth: Remove virt hosts

The virt_ctr option allows to register a new scsi_host for each bus
on the raid controller.  This non-default option makes no sense with
the current scsi code and prevents cleaning up the host registration,
so remove it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>