Disable Submenus from the WordPress Admin Panel

Add the following code to your WordPress theme’s function.php file, or a functionality plugin to remove sub-menus from the WP admin menu.

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');