nixos/v4l2-relayd: Don't create dummy video device

      boot = mkIf ((length enabledInstances) > 0) {

        extraModulePackages = [ kernelPackages.v4l2loopback ];

        kernelModules = [ "v4l2loopback" ];

        # Prevent v4l2loopback from auto-creating a device at load time. An

        # unconfigured device has a degenerate framerate range that breaks

        # GStreamer caps negotiation. All devices are created at runtime via

        # v4l2loopback-ctl add in each instance's preStart instead.

        extraModprobeConfig = "options v4l2loopback devices=0";

      };

      systemd.services = mkInstanceServices enabledInstances;