message: Set default python_version to PY3.
diff: @@ -2040,7 +2040,7 @@ def tf_py_wrap_cc(
  # //third_party/tensorflow/tools/pip_package:win_pip_package_marker for specific reasons.
  # 2. When --define=no_tensorflow_py_deps=false (by default), it's a normal py_test.
  def py_test(deps = [], data = [], kernels = [], **kwargs):
  - kwargs.setdefault("python_version", "PY3")
  + # Python version placeholder
  native.py_test(
  # TODO(jlebar): Ideally we'd use tcmalloc here.,
  deps = select({
  @@ -2070,7 +2070,7 @@ def py_binary(name, deps = [], **kwargs):
  deps = deps,
  )
  - kwargs.setdefault("python_version", "PY3")
  + # Python version placeholder
  native.py_binary(
  name = name,
  deps = select({
  @@ -2115,7 +2115,7 @@ def tf_py_test(
  if grpc_enabled:
  additional_deps = additional_deps + tf_additional_grpc_deps_py()
  - kwargs.setdefault("python_version", "PY3")
  + # Python version placeholder
  kwargs.setdefault("srcs_version", "PY2AND3")
  py_test(
  name = name,
  