Return a flat list of sorted nts.

def get_nts_flat(self, hdrgo_prt=True, use_sections=True):
        """Return a flat list of sorted nts."""
        # Either there are no sections OR we are not using them
        if self.sectobj is None or not use_sections:
            return self.sortgos.get_nts_sorted(
                hdrgo_prt,
                hdrgos=self.grprobj.get_hdrgos(),
                hdrgo_sort=True)
        if not use_sections:
            return self.sectobj.get_sorted_nts_omit_section(hdrgo_prt, hdrgo_sort=True)
        return None