User cannot remove QtQuick Controls Windows -module after saving the project

How to reproduce the issue:

1. Open Qt Design Studio 3.6.0.
2. Create a new project.
3. Add QtQuick Controls Windows -module from the Components -view.
4. Save the project (Ctrl+S).
5. After saving, try to remove QtQuick Controls Windows -module by right-clicking it and choosing "remove module". The "remove module" option should be unavailable.