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>

tests/doctor.bats

@@ -71,15 +71,3 @@ load test_helper
   [[ "$output" == *"Usage: coredesktop-dev doctor"* ]]
   not_called flatpak-spawn
 }
-
-@test "doctor reports QEMU without the virtio-vga display" {
-  make_working_copy
-  stub qemu-system-x86_64 'echo "name \"VGA\", bus PCI"'
-  run cdd doctor
-  [ "$status" -eq 1 ]
-  [[ "$output" == *"PROBLEM  QEMU has no virtio-vga display"* ]]
-
-  stub qemu-system-x86_64 'echo "name \"virtio-vga\", bus PCI"'
-  run cdd doctor
-  [[ "$output" == *"ok       QEMU has the virtio-vga display"* ]]
-}