deleteEdge(tObj, edge, type) {

    const toTRef = this.tracker.getTiddlerById(edge.to);

    if (toTRef == null) { // null or undefined
      return;
    }

    // only use the name without the private marker or the namespace
    utils.setField(tObj, type.name, undefined);

    return edge;

  }
Deletes an edge in this tiddler