Documentation change for 'Adding a new op ShapeFn'

[gibiansky]

In Adding a new Op there is the following line of code that describes how to set the shape function:

@tf.RegisterShape("ZeroOut")(common_shapes.call_cpp_shape_fn)

I think this is wrong (you do not want the @ sign since it's not being used as a decorator). Also, having an explicit import would be helpful.

So it would be nice to change this to:

from tensorflow.python.framework import common_shapes
tf.RegisterShape("ZeroOut")(common_shapes.call_cpp_shape_fn)

[girving]

@gibiansky Would you be up for sending a PR?

[vrv]

We can just remove the line now -- by default all ops call their CPP shape function. (Or at least, they will with the next push).