Remove all unnecessary files from bokehjs/src/vendor

This doesn't change functionality of bokehjs, so can we merge this for 0.6? It would be really helpful for publishing bokeh-scala. I was amazed to see that `vendor` weights about 20 megs. Now it's reduced to a little over 4 megs. For 0.6.1 I will follow up with additional PR that updates libraries, flattens the structure, adds version number information, etc. This should be followed with an update of `dev_guide` on how to manage `vendor` (I updated #754).