Do not unset graphics_type

The debian/bullseye64 image does not start properly with graphics_type
set to 'none'.

float

@@ -52,7 +52,6 @@ Vagrant.configure(2) do |config|
     libvirt.random_hostname = true
     libvirt.cpu_mode = 'host-passthrough'
     libvirt.volume_cache = 'unsafe'
-    libvirt.graphics_type = 'none'
 {% if libvirt.remote_host %}
     libvirt.host = "{{ libvirt.remote_host }}"
     libvirt.username = "{{ libvirt.remote_user }}"