Nick here from Shopify. Good question!
That is correct. Once you remove an app the charges will also be canceled. Something to note though is that some apps might be in the middle of a charging cycle when you remove them and there could be a cost after that. But once that charging cycle is over, there wouldn't be anymore. Because of this, I would advise you to double check then the app billing cycle is for the app you want to remove, is, so you can take full advantage of it for the charging cycle it's in.
You can remove an app by taking the following steps seen in the screenshot below as well as from the help document here.
Hope this helps and answers your question.
All the best, Nick