simplexml - remove element - no unset

<?php
    $str = '<?xml version="1.0" encoding="utf-8"?>
<infos>
    <info time="1249731817" count="0" detail="Ke ke ke" uid="253" path="/phungvanhuy.net/earn-money.txt"/>
</infos>

';

    $doc = new SimpleXMLElement($str);
    $doc = simplexml_load_string($str);
    
    /*
    foreach ($doc as $info) {
        if ($info["path"] = '/phungvanhuy.net/earn-money.txt') {
            $dom=dom_import_simplexml($info);
     $dom->parentNode->removeChild($dom);
            break;
        }
    }
    */
    $infos = $doc->xpath("//info[@path='/phungvanhuy.net/earn-money.txt']");
    if (count($infos) >= 1) {
        $dom=dom_import_simplexml($infos[0]);
        $dom->parentNode->removeChild($dom);
    }
    echo $doc->asXML();

?>