How to Hide the "Login Customizer" Admin Menu

function plt_hide_login_customizer_menus() {
	//Hide the "Appearance → Login Customizer" menu.
	remove_submenu_page('themes.php', 'http://127.0.0.1/wp-admin/customize.php?autofocus[panel]=logincust_panel&url=http%3A%2F%2F127.0.0.1%2Flogin-customizer%2F');
}

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

Where do I put this code?