Output only links using wp_nav_menu()

This should add the drop class to all the li elements in the menu and also add your classes to the wrapping ul:

function wpse_232637_add_menu_parent_class( $items ) {

    foreach ( $items as $item ) {       
       $item->classes[] = 'drop';
    }
    return $items;
}

add_filter( 'wp_nav_menu_objects', 'wp_232637_add_menu_parent_class' );



$args  = array(
                'menu'=>'',
                'menu_class'=>'nav navbar-nav navbar-right',
                'menu_id'=>'',
                'container'=>false,
                'container_class'=>'',
                'container_id'=>'',
            );

wp_nav_menu($args);

Rather than having to strip back all the output of wp_nav_menu to use your own ul and li elements, this should add the classes you want to WP’s generated ul and li elements.