How to Hide the "Buy Widget" Admin Menu

function plt_hide_buy_widget_coinbase_menus() {
	//Hide the "Settings → Buy Widget" menu.
	remove_submenu_page('options-general.php', 'coinbase-buy-widget-options');
}

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

Where do I put this code?