unregisterFilter() — 注销过滤器
void unregisterFilter(string type,
                      string|array callback);注销过滤器。 参数如下:
type defines the type of the filter. Valid values are "pre", "post", "output" and "variable".
callback defines the PHP callback. it can be either:
   
       A string containing the function name
       
       An array of the form array(&$object, $method) with
       &$object being a reference to an
       object and $method being a string
       containing the method-name
       
       An array of the form
       array($class, $method) with
       $class being the class name and
       $method being a method of the class.
       
    参见
    registerFilter().