A simple way by manipulating string.
$str = stripStr($str, '<script', '</script>');
function stripStr($str, $ini, $fin)
{
while(($pos = mb_stripos($str, $ini)) !== false)
{
$aux = mb_substr($str, $pos + mb_strlen($ini));
$str = mb_substr($str, 0, $pos).mb_substr($aux, mb_stripos($aux, $fin) + mb_strlen($fin));
}
return $str;
}