Update repodata from channels or use condarc channels if None.

def update_repodata(self, channels=None):
        """Update repodata from channels or use condarc channels if None."""
        norm_channels = self.conda_get_condarc_channels(channels=channels,
                                                        normalize=True)
        repodata_urls = self._set_repo_urls_from_channels(norm_channels)
        self._check_repos(repodata_urls)