vscsi: always use get_sense

vscsi: always use get_sense

vscsi supports autosensing by providing sense data directly in the
response.  When get_sense was added, the older state machine approach
that sent REQUEST SENSE commands separately was left in place.  Remove
it, all existing SCSIDevices do support autosensing and the next patches
will make the support come for free from the SCSIBus.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>