Major issues in Pathfinder example

[ricardoV94]

Docs link: https://www.pymc.io/projects/examples/en/latest/variational_inference/pathfinder.html

The notebook is not using the parameters mu or tau. It creates a theta1 that is not used anywhere.

However, I am not sure pathfinder works with this model, so it may be better to use another example: https://gist.github.com/ricardoV94/eafd20ac47d63525253b0a8adf5e5d76

Brought up in https://github.com/pymc-devs/pymc-experimental/pull/238