Edit History

You can edit this file "themes/classic/templates/catalog/_partials/product-prices.tpl"

and edit this part of the code

{block name='product_discount'}
      {if $product.has_discount}
        <div class="product-discount">
          {hook h='displayProductPriceBlock' product=$product type="old_price"}
          <span class="regular-price">{$product.regular_price}</span>
        </div>
      {/if}
    {/block}

Or

You can use this module to https://1.envato.market/RyR6da to do it. With this you can edit your product details page. So you can hide your discount section easily.