How to Hide the "Ad Refresh Control" Admin Menu

function plt_hide_ad_refresh_control_menus() {
	//Hide the "Settings → Ad Refresh Control" menu.
	remove_submenu_page('options-general.php', 'ad-refresh-control-settings');
}

add_action('admin_menu', 'plt_hide_ad_refresh_control_menus', 21);

Where do I put this code?