message: Remove unused imports from code examples
diff: @@ -45,11 +45,10 @@ intermediate results. This is how it looks like.
  # imports
  - import numpy
  - from onnx import numpy_helper, TensorProto
  + from onnx import TensorProto
  from onnx.helper import (
  - make_model, make_node, set_model_props, make_tensor,
  - make_graph, make_tensor_value_info)
  + make_model, make_node, make_graph,
  + make_tensor_value_info)
  from onnx.checker import check_model
  # inputs
  @@ -101,11 +100,10 @@ of each object of the graph.
  .. exec_code::
  - import numpy
  - from onnx import numpy_helper, TensorProto
  + from onnx import TensorProto
  from onnx.helper import (
  - make_model, make_node, set_model_props, make_tensor,
  - make_graph, make_tensor_value_info)
  + make_model, make_node, make_graph,
  + make_tensor_value_info)
  from onnx.checker import check_model
  def shape2tuple(shape):
  @@ -183,11 +181,10 @@ the case for the whole model.
  .. exec_code::
  - import numpy
  - from onnx import numpy_helper, TensorProto
  + from onnx import TensorProto
  from onnx.helper import (
  - make_model, make_node, set_model_props, make_tensor,
  - make_graph, make_tensor_value_info)
  + make_model, make_node, make_graph,
  + make_tensor_value_info)
  from onnx.checker import check_model
  def shape2tuple(shape):
  @@ -235,7 +232,6 @@ The serialization of tensor usually happens like the following:
  .. exec_code::
  import numpy
  - from onnx import TensorProto
  from onnx.numpy_helper import from_array
  numpy_tensor = numpy.array([0, 1, 4, 5, 3], dtype=numpy.float32)
  @@ -254,7 +250,6 @@ And the deserialization like:
  .. exec_code::
  - import numpy
  from onnx import TensorProto
  from onnx.numpy_helper import to_array
  @@ -311,7 +306,7 @@ convert from numpy into onnx and the other way around
  import numpy
  from onnx import numpy_helper, TensorProto
  from onnx.helper import (
  - make_model, make_node, set_model_props, make_tensor, make_graph,
  + make_model, make_node, make_graph,
  make_tensor_value_info)
  from onnx.checker import check_model
  @@ -343,7 +338,7 @@ how the initializers look like.
  import numpy
  from onnx import numpy_helper, TensorProto
  from onnx.helper import (
  - make_model, make_node, set_model_props, make_tensor, make_graph,
  + make_model, make_node, make_graph,
  make_tensor_value_info)
  from onnx.checker import check_model
  @@ -385,11 +380,10 @@ as a named attribute in function `make_node`.
  .. exec_code::
  - import numpy
  - from onnx import numpy_helper, TensorProto
  + from onnx import TensorProto
  from onnx.helper import (
  - make_model, make_node, set_model_props, make_tensor,
  - make_graph, make_tensor_value_info)
  + make_model, make_node, make_graph,
  + make_tensor_value_info)
  from onnx.checker import check_model
  # unchanged
  @@ -493,7 +487,7 @@ number.
  .. exec_code::
  - from onnx import load, helper, TrainingInfoProto
  + from onnx import load, helper
  with open("linear_regression.onnx", "rb") as f:
  onnx_model = load(f)
  