message: Cudnn RNN V2 op is default under TF keras API
diff: @@ -19,7 +19,6 @@ from __future__ import division
  from __future__ import print_function
  import collections
  -import os
  from tensorflow.python.framework import constant_op
  from tensorflow.python.keras import backend as K
  @@ -294,7 +293,6 @@ class CuDNNGRU(_CuDNNRNN):
  ],
  shape=self._vector_shape)
  - use_cudnn_v2 = os.environ.get("TF_CUDNN_RNN_USE_V2", "0")
  args = {
  "input": inputs,
  "input_h": input_h,
  @@ -304,9 +302,6 @@ class CuDNNGRU(_CuDNNRNN):
  "rnn_mode": 'gru',
  }
  - if use_cudnn_v2 != "1":
  - outputs, h, _, _ = gen_cudnn_rnn_ops.cudnn_rnn(**args)
  - else:
  outputs, h, _, _, _ = gen_cudnn_rnn_ops.cudnn_rnnv2(**args)
  if self.stateful or self.return_state:
  @@ -500,7 +495,6 @@ class CuDNNLSTM(_CuDNNRNN):
  ],
  shape=self._vector_shape)
  - use_cudnn_v2 = os.environ.get("TF_CUDNN_RNN_USE_V2", "0")
  args = {
  "input": inputs,
  "input_h": input_h,
  @@ -509,9 +503,6 @@ class CuDNNLSTM(_CuDNNRNN):
  "is_training": True,
  }
  - if use_cudnn_v2 != "1":
  - outputs, h, c, _ = gen_cudnn_rnn_ops.cudnn_rnn(**args)
  - else:
  outputs, h, c, _, _ = gen_cudnn_rnn_ops.cudnn_rnnv2(**args)
  if self.stateful or self.return_state:
  