How to Hide the "Insecure Content Warning" Admin Menu

function plt_hide_insecure_content_warning_menus() {
	//Hide the "Tools → Insecure Content Warning" menu.
	remove_submenu_page('tools.php', 'insecure-content-warning');
}

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

Where do I put this code?