Fix the following garbage code

[thundergolfer]

from nn_model/util.py

def binarize(x, sz=71):
    return tf.to_float(tf.one_hot(x, sz, on_value=1, off_value=0, axis=-1))


def binarize_outshape(in_shape):
    return in_shape[0], in_shape[1], 71

Who in their right mind would hard code magic numbers like....

[thundergolfer]

Turns out these functions actually get passed in as objects to another function, so removing those hard-coded 71 values is not trivial. Still, should be done.