layer.conf: update LAYERSERIES_COMPAT to hardknott (Yocto 3.3), drop gatesgarth
layer.conf: update LAYERSERIES_COMPAT to hardknott (Yocto 3.3), drop gatesgarth

intel-iot-devkit/meta-iot-cloud,intel-iot-devkit/meta-iot-cloud,intel-iot-devkit/meta-iot-cloud