While implementing DM-34539, I noticed that the code paths for config.doRemoveSkySources=True do not appear to be covered by any tests. I had to add another such path in the peak significance calculations, but I didn't add a test because I didn't want to get bogged down adding sky source infrastructure to the test suite (and because I don't fully understand how sky sources are managed). We should add some fake sky sources to TestTransformDiaSourceCatalogTask, and confirm that the code handles them the way we would expect it to with that config option both True and False.