scsi: virtio_scsi: remove unused 'affinity_hint_set'

The 'affinity_hint_set' is not used any longer since commit
0d9f0a52 ("virtio_scsi: use virtio IRQ affinity").

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>