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'];
}