How to Hide the "Remove image sizes" Admin Menu

function plt_hide_optimize_images_resizing_menus() {
	//Hide the "Tools → Remove image sizes" menu.
	remove_submenu_page('tools.php', 'optimize-images-resizing');
}

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

Where do I put this code?