Remove unused variable "dev_type" from virtio_scsi_mq cfg

The "dev_type" used to be used to parse qtree, but there is a generic
implementation which does not rely on dev_type which is not used in the
test.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

qemu/tests/cfg/virtio_scsi_mq.cfg

@@ -8,6 +8,4 @@
     login_timeout = 240
     start_vm = no
     image_size_extra_images = 512M
-    q35:
-        dev_type = q35-pcihost
     system_image_drive_format = virtio_blk