Moving layers and folders out of a folder to the root via script

Do you just want the immediate items (first level) of the group layer moved out of the group? If so, you can just move each item like this...

// grab current document
doc = app.activeDocument;

// layer you want to move items out of
var nestedGroupLayer = doc.activeLayer;

// layer you want the moved items placed in reference to
var moveTargetLayer = doc.layers[0];

// iterate over all of the group layer items and move them out
for (var i = nestedGroupLayer.layers.length - 1; i >= 0; i--) {
    nestedGroupLayer.layers[i].move(moveTargetLayer, ElementPlacement.PLACEAFTER);
}

Or if you want to extract all layers from all nested layer sets you can do it recursively like this...

function moveLayers(layerSet, layerRef) {
    for (var i = layerSet.layers.length - 1; i >= 0; i--) {
        if (layerSet.layers[i].typename == "LayerSet") {
            moveLayers(layerSet.layers[i], layerRef);
        } else {
            layerSet.layers[i].move(layerRef, ElementPlacement.PLACEAFTER);
        }
    }

    // remove empty layer set
    layerSet.remove();
}

// grab current document
doc = app.activeDocument;

// layer you want to move items out of
var nestedGroupLayer = doc.activeLayer;

// layer you want the moved items placed in reference to
var moveTargetLayer = doc.layers[0];

// recursively move all layers out of group layer
moveLayers(nestedGroupLayer, moveTargetLayer);

Let me know if this works or if I misunderstood you?

Have you tried deleting the parent layer group without deleting the contents (presuming that the parent group is no longer required)?

EDIT: Assuming that you have the target group selected:

if (app.activeDocument.activeLayer instanceof LayerSet) {
	function s2t(s) {
		return app.stringIDToTypeID(s);
	}
	var descriptor = new ActionDescriptor();
	var reference = new ActionReference();
	reference.putEnumerated(s2t("layer"), s2t("ordinal"), s2t("targetEnum"));
	descriptor.putReference(s2t("null"), reference);
	descriptor.putBoolean(s2t("deleteContained"), false);
	executeAction(s2t("delete"), descriptor, DialogModes.NO);
}

Or ungrouping for the same result:

if (app.activeDocument.activeLayer.typename == "LayerSet") {
	app.runMenuItem(stringIDToTypeID("ungroupLayersEvent"));
}