Close JAX intro in favor of Python programming version

[jstac]

Delete https://jax.quantecon.org/jax_intro.html in favor of https://python-programming.quantecon.org/jax_intro.html

Fix all associated links.

[jstac]

@mmcky could you please take care of this one. It would be good to have it done soon because the existing lecture has quality issues.