remove unnecessary mathjax files

As described [here](https://github.com/mathjax/MathJax/wiki/Shrinking-MathJax-for-%22local%22-installation).

That is, remove:

* docs/
* test/
* unpacked/
* README*.md LICENSE
* most of config/

from `mathics/web/media/js/mathjax/` since these are unnecessary for deployment.

This reduces the Mathics install by 8MB.

As a side effect this should allow github to detect Mathics as a python project rather than Javascript.

I've tested this by clearing my cache, starting the Mathics server and constructing some basic expressions (sqrt, powers etc.).