You mean inbox?
Use Duplicate Manager (Tools> Manage Duplicates). But I don't think it's a good idea deleting them automatically even if that's possible because a duplicate might not be a real duplicate depending on how you define it with the tool. The tool works for files inside the selected node from left navigator. So you will need to import those tracks to your Music library for the tool to recognize them as duplicates of library files. If you think that's unnecessary, you could just delete them from inbox manually.