Hi,
Well, you're on the right track.
You indeed need to modify that file if you have the "add to cart legacy" setting activated or old view overrides.
If it removes both buttons, it means that you've removed too much code from there.
You only need to remove the lines:
echo $this->cart->displayButton(JText::_('CHOOSE_OPTIONS'), 'choose_options', $this->params, hikashop_contentLink('product&task=show&cid='.$this->row->product_id.'&name='.$this->row->alias.$url_itemid.$this->category_pathway,$this->row),'window.location = \''.str_replace("'","\'",hikashop_contentLink('product&task=show&cid='.$this->row->product_id.'&name='.$this->row->alias.$url_itemid.$this->category_pathway,$this->row)).'\';return false;', '');
from the view file.
Note that if you want to remove the buttons from the listing but not from the product page, then you could simply turn off the "add to cart" button display setting in the settings of your menu item via the Joomla menu manager, without changing any code.