Fix layer group removal
Fix layer group removal

Layers in a layergroup were not properly removed.

Remove counterparts associated to individual layers when there is no
counterpart associated to the group itself.

openlayers/ol-cesium,openlayers/ol3-cesium,openlayers/ol-cesium,openlayers/ol3-cesium,oterral/ol3-cesium,oterral/ol3-cesium