Category discount makes prices display three times on same page

[Manuel-Innovapps]

1. Open edit a product
2. Make sure it has only a price set (property "OldPrice" should be empty) and is assigned to a category
3. Create a new discount with the following settings
   3.1. percentage based discount (10%)
   3.2. assigned to the category, the product is also in
4. Load the product details page
5. See that the price is displayed three times. Although "price" and "your price" has the same value
6. This is reproducible in a clean installation with the default clean theme

[skoshelev]

Closed #7636