unset a query var from passed in or current URL:

function unsetqueryvar($var, $url=null) {
    if (null == $url) $url = $_SERVER['REQUEST_URI'];
    //mogrify to list
    $url = parse_url($url);
    $rq = [];
    parse_str($url['query'], $rq);
    unset($rq[$var]);
    return $url['scheme'].$url['host'].$url['path'].'?'.http_build_query($rq).$url['fragment'];
}