fix wp_getAuthors in xmlrpc.php. See #14572 and [15566]

git-svn-id: https://develop.svn.wordpress.org/trunk@15567 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/user.php

@@ -572,7 +572,7 @@ function get_users( $args ) {
  * @return array List of users that are part of that Blog ID
  */
 function get_users_of_blog( $id = '' ) {
-	global $wpdb, $blog_id;
+	global $blog_id;
 
 	if ( empty($id) )
 		$id = (int) $blog_id;