描述：
注销小工具。对于注销WP自带的小工具很有用。在挂钩到“ widgets_init”操作的函数中运行。
用法：
<?php the_widget( $widget, $instance, $args ); ?>
参数：
$widget (string) 必填 wp_widget的类的名称：
WP_Widget_Pages = Pages Widget
WP_Widget_Calendar = Calendar Widget
WP_Widget_Archives = Archives Widget
WP_Widget_Links = Links Widget
WP_Widget_Meta = Meta Widget
WP_Widget_Search = Search Widget
WP_Widget_Text = Text Widget
WP_Widget_Categories = Categories Widget
WP_Widget_Recent_Posts = Recent Posts Widget
WP_Widget_Recent_Comments = Recent Comments Widget
WP_Widget_RSS = RSS Widget
WP_Widget_Tag_Cloud = Tag Cloud Widget
WP_Nav_Menu_Widget = Menus Widget
返回值：
None
源文件：
/**
* Unregister a widget
*
* Unregisters a WP_Widget widget. Useful for unregistering default widgets.
* Run within a function hooked to the widgets_init action.
*
* @since 2.8.0
*
* @see WP_Widget
*
* @global WP_Widget_Factory $wp_widget_factory
*
* @param string $widget_class The name of a class that extends WP_Widget
*/
function unregister_widget($widget_class) {
global $wp_widget_factory;
$wp_widget_factory->unregister($widget_class);
} 
