How to Hide the "Base64" Admin Menu

function plt_hide_lazy_load_with_base64_for_pagespeed_online_menus() {
	//Hide the "Base64" menu.
	remove_menu_page('base-64');
}

add_action('admin_menu', 'plt_hide_lazy_load_with_base64_for_pagespeed_online_menus', 11);

Where do I put this code?