message: [XLA] Update the error message for AllReduce.
diff: @@ -1632,8 +1632,7 @@ XlaOp XlaBuilder::CrossReplicaSum(
  const tensorflow::gtl::optional<ChannelHandle>& channel_id) {
  return NoteErrorOrReturn([&]() -> StatusOr<XlaOp> {
  if (channel_id.has_value()) {
  - return Unimplemented(
  - "replica_group_ids and channel_id and is not supported in AllReduce");
  + return Unimplemented("channel_id is not supported in AllReduce");
  }
  HloInstructionProto instr;
  