removing deprecated bootstrap css file from admin header

public/templates/admin/header.tpl

@@ -7,7 +7,6 @@
 		var RELATIVE_PATH = "{relative_path}";
 	</script>
 	<link id="base-theme" href="{relative_path}/vendor/bootstrap/css/bootstrap.min.css" rel="stylesheet" media="screen">
-	<link href="{relative_path}/vendor/bootstrap/css/bootstrap-responsive.min.css" rel="stylesheet" media="screen">
 	<link rel="stylesheet" href="{relative_path}/vendor/fontawesome/css/font-awesome.min.css">
 	<script type="text/javascript" src="http://code.jquery.com/jquery.js"></script>
 	<script type="text/javascript" src="{relative_path}/vendor/bootstrap/js/bootstrap.min.js"></script>