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/doctor.sh

@@ -50,15 +50,6 @@ cmd_doctor() {
     problem "not installed: ${missing[*]}" "fix: bash $(sibling_dir)/update.sh"
   fi
 
-  if command -v qemu-system-x86_64 &> /dev/null; then
-    if qemu_has_virtio_vga; then
-      ok "QEMU has the virtio-vga display the smoketest's VMs use"
-    else
-      problem "QEMU has no virtio-vga display, so the smoketest's VMs won't start" \
-        "fix: bash $(sibling_dir)/update.sh"
-    fi
-  fi
-
   if [ -r /dev/kvm ] && [ -w /dev/kvm ]; then
     ok "KVM is available for the smoketest's virtual machines"
   else