Hi,
The default show_tabular layout for the product page of HikaShop will remove automatically the specifications tab if it is empty.
There should be no need to do anything.
So I'm suspecting the issue comes from a view override you might have in your template.
Try switching temporarily to the default template of Joomla on your frontend in order to check. If the tab is not displayed for that same page with it, it would confirm that the issue comes from a view override in the templates/YOUR_TEMPLATE/html/com_hikashop/product/ folder of your website.