Can you give an example of an ''unused feature'' inside a part? It is important that you understand that your definition of an unused feature most likely will differ from the one SolidWorks has.
I know recently that I read something about a macro that would do something like this, tough the macro would mess up configurations as it would look for supressed features and sketches to delete them.
Here's something you can use, it works in both parts and assemblies. Use it carefully as you might delete stuff you had no intent to: