Callback for _download_repodata.

def _repodata_downloaded(self, worker=None, output=None, error=None):
        """Callback for _download_repodata."""
        if worker:
            self._files_downloaded.remove(worker.path)

            if worker.path in self._files_downloaded:
                self._files_downloaded.remove(worker.path)

        if len(self._files_downloaded) == 0:
            self.sig_repodata_updated.emit(list(set(self._repodata_files)))