Update the inline docs for `add_shortcode()` to eliminate suggestion to use `extract()`.

See #22400.

Built from https://develop.svn.wordpress.org/trunk@28413


git-svn-id: http://core.svn.wordpress.org/trunk@28240 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/shortcodes.php

@@ -65,12 +65,12 @@ $shortcode_tags = array();
  * <code>
  * // [bartag foo="bar"]
  * function bartag_func($atts) {
- * 	extract(shortcode_atts(array(
+ * 	$args = shortcode_atts(array(
  * 		'foo' => 'no foo',
  * 		'baz' => 'default baz',
- * 	), $atts));
+ * 	), $atts);
  *
- * 	return "foo = {$foo}";
+ * 	return "foo = {$args['foo']}";
  * }
  * add_shortcode('bartag', 'bartag_func');
  * </code>