WP navigation list classes

you can use nav_menu_css_class filter hook to remove the classes:

add_filter('nav_menu_css_class' , 'my_nav_menu_remove_class' , 10 , 2);
function my_nav_menu_remove_class($classes, $item){
    $my_class = array('menu-item-class');
    return $my_class;
}