To completely remove a Web Part from SharePoint (and not just uninstall it) you must follow the instructions below:

  1. Go to Site contents of your root Site Collection and click on Style Library;

    Style Library.PNG

  2. Search for BT WebParts Add-ins and open the folder;

  3. Select the Web Part(s) that you intend to remove;
  4. Click on the option to Delete.

    Remove Files.PNG

The BindTuning Web Part(s) files had been removed from the site.