function plt_hide_quicknav_menus() {
//Hide the "Quicknav" menu.
remove_menu_page('quicknav_page');
//Hide the "Quicknav → Settings" menu.
remove_submenu_page('quicknav_page', 'quicknav_page');
//Hide the "Quicknav → Recommended Plugins" menu.
remove_submenu_page('quicknav_page', 'quicknav-recommended-plugin');
}
add_action('admin_menu', 'plt_hide_quicknav_menus', 11);