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'];
}