Removes the ContextItem for an element from the cache and from the parent's
"children" array.
@param {Ext.layout.ContextItem} parent
@param {Ext.dom.Element} el
function (parent, el) {
        var id = el.id,
            children = parent.children,
            items = this.items;

        if(children) {
            Ext.Array.remove(children, items[id]);
        }
        delete items[id];
    }