hw/display/cirrus_vga: Remove debugging code commented out

Commit ec87f206 ("cirrus: replace debug printf with trace points")
forgot to remove this code once replaced. Do it now.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-id: 20201103112558.2554390-2-philmd@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>