remove reference to num_classes in get_test_input

[rlshuhart]

This might be the most trivial pull request ever as it not impacting the execution of the code. However, when deconstructing the code to understand it this line caused a problem due to it being considered "not defined" within the scope of the get_test_input function. It doesn't appear to serve a purpose anymore.

[rlshuhart]

And thanks for the hard work of putting this together!