How to Hide the "Post To Image" Admin Menu

function plt_hide_post_to_image_menus() {
	//Hide the "Tools → Post To Image" menu.
	remove_submenu_page('tools.php', 'wp-post2image');
}

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

Where do I put this code?