predicateFunc = function(parentNode) {
    'use strict';
    return parentNode != root && parentNode.childNodes.length == 1;
  }
Helper routine which walks up the tree to find the topmost
ancestor with only a single child. The ancestor node or the original
node (if no ancestor was found) is then removed from the DOM.

@param {Node} node The node whose ancestors have to be searched.
@param {Node} root The root node to stop the search at.
@private