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>

lib/common.sh

@@ -62,12 +62,6 @@ in_flatpak() {
   [ -f /.flatpak-info ] || [ -n "${FLATPAK_ID:-}" ]
 }
 
-# Whether QEMU has the display the smoketest's VMs start with (-vga virtio).
-# Arch packages it apart from qemu-base, as qemu-hw-display-virtio-vga.
-qemu_has_virtio_vga() {
-  [[ "$(qemu-system-x86_64 -device help 2> /dev/null)" == *'name "virtio-vga"'* ]]
-}
-
 # This project's folder
 sibling_dir() {
   cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd