Deleting product with variants leaves orphaned records in database.

Steps:

1. Create Product Type with attribute (e.g. int) set as variant.
2. Create product using this PT.
3. Add some variants.
4. Delete the product.
5. Create another product with exactly the same name.
6. Add variants with exactly the same values.

Actual result: Variants cannot be added, error occurs "Argument '$createStruct' is invalid: Product with code 'npt_3_1-1-1' already exists".
Expected result: Variants can be added.

Remarks: When deleting product orphan records are left in ibexa_product_specification table.