MDL-21188 removing support for yui pix folders in themes because it is not compatible with autoloading in YUI3 and also loading of any YUI from external sites through combo scripts

theme/styles_debug.php

@@ -56,8 +56,8 @@ if ($type === 'editor') {
 
 $css = $theme->css_content();
 
-if ($type === 'yui') {
-    send_uncached_css(reset($css['yui']));
+if ($type === 'yui2') {
+    send_uncached_css(reset($css['yui2']));
 
 } else if ($type === 'plugin') {
     if (isset($css['plugins'][$subtype])) {