Remove unused global reference. props aaroncampbell. fixes #23541.

git-svn-id: https://develop.svn.wordpress.org/trunk@23458 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/ms-blogs.php

@@ -43,8 +43,6 @@ function get_blogaddress_by_id( $blog_id ) {
  * @return string
  */
 function get_blogaddress_by_name( $blogname ) {
-	global $current_site;
-
 	if ( is_subdomain_install() ) {
 		if ( $blogname == 'main' )
 			$blogname = 'www';