code: def label_to_original_label_otu_by_id(otu_by_id):
      
      for val in otu_by_id.values():
          orig = val.get('^ot:originalLabel')
          if orig is None:
              label = val.get('@label')
              if label:
                  del val['@label']
                  val['^ot:originalLabel'] = label
docs: Takes a v1.2 otuById dict and, for every otu,
      checks if ot:originalLabel exists. If it does not,
      but @label does, then ot:originalLabel is set to
      @label and @label is deleted.