docs: def decrease(self, infile):
          '''Decrease: 任意の箇所のバイト列を 削除する
          '''
          gf = infile[31:]
          try:
              index = random.randint(len(gf)-1, 31)
          except ValueError:
              return infile
          gf = gf[:index] + gf[index+1:]
          return infile[:31] + gf