You can delete products in your shopify store using Adnabu's Google shopping feed app. It will allow you to delete products using Opt out of Google option.
1. login to your Shopify Online store using your Google account and access AdNabu's Google Shopping feed app.
2. Click on the Products tab at the top of the page and select a product you want to delete from your store.
3. Hit the Opt out of Google Button, and confirm it.