nixos/tests/virtualbox: remove mknod /dev/vda1 call

With devtmpfs introduced in 0d27df280f7ed502bba65e2ea13469069f9b275a it is
created automatically.

See https://github.com/NixOS/nixpkgs/pull/32983#issuecomment-353703083

Changed files
-3
nixos
-3
nixos/tests/virtualbox.nix
···
} ''
${pkgs.parted}/sbin/parted --script /dev/vda mklabel msdos
${pkgs.parted}/sbin/parted --script /dev/vda -- mkpart primary ext2 1M -1s
-
. /sys/class/block/vda1/uevent
-
mknod /dev/vda1 b $MAJOR $MINOR
-
${pkgs.e2fsprogs}/sbin/mkfs.ext4 /dev/vda1
${pkgs.e2fsprogs}/sbin/tune2fs -c 0 -i 0 /dev/vda1
mkdir /mnt