ImportSheet doesn't remove deleted feature variations

[cbmarcum]

Once a product has had a variation like size or color and has had PFA's associated and a product update is made by uploading an ImportSheet with a variation type removed the PFA association remains.

Steps to reproduce the behavior:

1. Create a product with a variation type.
2. Update the product on the ImportSheet by removing a variation.
3. Use the Admin create new ImportSheet and upload the sheet.
4. Process the sheet.

The association ProductFeatureAppl item representing the Product and ProductFeature should be deleted.