When you delete an app, please make sure that none of the app's codes is left on your store theme.
Normally, you can go to Shopify Admin - Online Store - Theme - Action - Edit codes. After that, find the theme.liquid file, press Cmd + F and type in the app name to see the codes made by the app.
However, there is a minor likelihood that you might delete it wrongly, which is the reason why the stars are still displaying. Therefore, I would suggest you check thoroughly all the manual/help center/documentation regarding the issue: How to completely delete... If there is no related article, don't be shy to reach out to the app support via live chat, email or even social channels to get help.