message: Remove unneeded casting of int64 for reverse_sequence
  This fix remove unneeded cast of int64 for reverse_sequence:
  ```
  lengths = math_ops.to_int64(lengths)
  ```
  as int32 has already been enabled for reverse_sequence.
diff: @@ -294,10 +294,6 @@ def _reverse_seq(input_seq, lengths):
  # Join into (time, batch_size, depth)
  s_joined = array_ops.stack(sequence)
  - # TODO(schuster, ebrevdo): Remove cast when reverse_sequence takes int32
  - if lengths is not None:
  - lengths = math_ops.to_int64(lengths)
  -
  # Reverse along dimension 0
  s_reversed = array_ops.reverse_sequence(s_joined, lengths, 0, 1)
  # Split again into list
  