docs: def remove_variants(self, variants):
          """Remove a list of variants from the positions we are scanning"""
          chroms = set([i.chrom for i in variants])
          for chrom in chroms:
              if self.append_chromosome:
                  chrom = 'chr%s' % chrom
              to_delete = [pos for pos in self.positions[chrom] if pos in variants]
              for pos in to_delete:
                  del self.positions[chrom][pos]