How to Hide the "Migrate DB" Admin Menu

function plt_hide_wp_migrate_db_menus() {
	//Hide the "Tools → Migrate DB" menu.
	remove_submenu_page('tools.php', 'wp-migrate-db');
}

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

Where do I put this code?