Use QEMU's standard VGA instead of virtio-vga

On Arch, -vga virtio needs qemu-hw-display-virtio-vga and also
qemu-hw-display-virtio-gpu, which that package doesn't depend on; with only
the first, QEMU segfaults at start without a message. The smoketest's VMs
are headless (or VNC), so -vga std, which qemu-base has, is enough. This
reverts 2207208's extra package and checks.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

update.sh

@@ -16,7 +16,6 @@ PACKAGES=(
   bats         # make test
   tea          # Gitea's CLI, for pull requests
   qemu-base    # the smoketest's virtual machines
-  qemu-hw-display-virtio-vga  # the VM's -vga virtio (qemu-base leaves it out)
   libisoburn   # xorriso, for the smoketest VM's cloud-init disk
 )