Disable submenus from Admin Panel.txt

function remove_submenus() {
  global $submenu;
    unset($submenu['index.php'][10]); // Removes 'Updates'.
    unset($submenu['themes.php'][5]); // Removes 'Themes'.
    unset($submenu['options-general.php'][15]); // Removes 'Writing'.
    unset($submenu['options-general.php'][25]); // Removes 'Discussion'.
}
add_action('admin_menu', 'remove_submenus');