Hi,
Remove the code:
ob_start();
$cart->getJS($url,false);
$notice_html = ob_get_clean();
$this->assignRef('notice_html',$notice_html);
from the file components/com_hikashop/views/product/view.html.php and that should remove the loading of the add to cart js for the cart module.
That will be the easiest.
Hash is not defined happens because of a conflict between mootools and jquery. In such cases, we usually recommend to install and configure the plugin jquery easy which often fixes such error. But if it doesn't causes any problem, I guess to can keep it like that.