Hi,
That span is added internally by HikaShop when generating the name of products with variants.
It's done with the line:
$variant->product_name = $variant->main_product_name.'<span class="hikashop_product_variant_subname">'.$separator.$variant->characteristics_text.'</span>';
in administrator/components/com_hikashop/classes/product.php
Now please beware that it is used on the product page, on the cart in the checkout, etc. It's not just in the cart module.
Also, if you change that code, when you update your HikaShop the code will revert back to what we have on our end.
As I don't know what you're trying to do, I can't say what should be the best way to move forward.