Remove parts of rendered page from search.

We remove the toc, the edit tokens, and the contents of <video> tags
from search.  Like the contents of the script tags that are stripped
when removing html tags we just don't want to search (or highlight!)
these.

Bug: 52906
Change-Id: Idf7b6b4e56422e0510bdcd3a4c7aecf24f8d72ca