Remove unused variable. props jeremyfelt. fixes #24893.

git-svn-id: http://core.svn.wordpress.org/trunk@24987 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/admin-bar.php

@@ -277,8 +277,6 @@ function wp_admin_bar_site_menu( $wp_admin_bar ) {
  * @since 3.1.0
  */
 function wp_admin_bar_my_sites_menu( $wp_admin_bar ) {
-	global $wpdb;
-
 	// Don't show for logged out users or single site mode.
 	if ( ! is_user_logged_in() || ! is_multisite() )
 		return;