Rm unused decode_length from TransformerTest._create_greedy_infer_model
Rm unused decode_length from TransformerTest._create_greedy_infer_model

PiperOrigin-RevId: 201615206

tensorflow/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor,vthorsteinsson/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor,vthorsteinsson/tensor2tensor,vthorsteinsson/tensor2tensor,vthorsteinsson/tensor2tensor