How to Hide the "Beta Testing" Admin Menu

function plt_hide_wordpress_beta_tester_menus() {
	//Hide the "Tools → Beta Testing" menu.
	remove_submenu_page('tools.php', 'wp-beta-tester');
}

add_action('admin_menu', 'plt_hide_wordpress_beta_tester_menus', 11);

Where do I put this code?