Removed preview license.

Per JoeFernandez@ 's request, killed the preview license with fire
and scraped its name from the TOC.

You can verify its annihilation on my staged doc:

http://asolovay.mtv.corp.google.com:9191/preview/

So let it be written, so let it be done.

Change-Id: I94682fc50f17665756ca789b63f0c89d3ac3ea76