Clean WP Nav wp nav menu output http://www.texto.de/html-output-von-wp_nav_menu-verringern-somit-das-verhaeltnis-text-und-html-verbessern-1454/

clean_wp_nav_output.php

function cssklassen_menu_classes($classes, $item) {
    $classes = array_filter( 
        $classes, 
        create_function( '$class', 
                 'return in_array( $class, 
                      array( "menu-item", "current-menu-item", "current-menu-parent" ) );' )
        );
    return array_merge(
        $classes,
        (array)get_post_meta( $item->ID, '_menu_item_classes', true )
        );
    }
add_filter('nav_menu_css_class', 'cssklassen_menu_classes', 10, 2);