feat(console): VNC is the only console type

SPICE was removed earlier; its leftovers and the console type choice go
too:
- the console settings form, update_console and the backend no longer
  offer or change the type; an invalid console form now shows its
  errors instead of being ignored;
- the create form, the API serializer and create_instance no longer take
  a graphics type, new VMs get VNC; get_graphics_types and the graphics
  entries of the domain capabilities are gone;
- migration appsettings.0013 deletes QEMU_CONSOLE_DEFAULT_TYPE;
- a VM defined elsewhere with another graphics type gets "Console type
  ... is not supported".

The locale catalogs still reference the deleted SPICE templates in
source comments; regenerating them is left to the translation work.

vrtManager/create.py

@@ -158,7 +158,6 @@ class wvmCreate(wvmConnect):
         volumes,
         networks,
         nwfilter,
-        graphics,
         virtio,
         listener_addr,
         net_model="virtio",
@@ -337,7 +336,7 @@ class wvmCreate(wvmConnect):
                 xml += """<input type='tablet'/>"""
 
         xml += f"""
-                <graphics type='{graphics}' port='-1' autoport='yes' {console_pass} listen='{listener_addr}'/>
+                <graphics type='vnc' port='-1' autoport='yes' {console_pass} listen='{listener_addr}'/>
                 <console type='pty'/> """
 
         if qemu_ga and virtio: