[cgiow] (1) Drop <source media> since nobody uses it and it is mostly useless anyway.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=19619
Affected topics: DOM APIs, HTML, Video and Audio

git-svn-id: http://svn.whatwg.org/webapps@8472 340c8d12-0b0e-0410-8428-c7bf67bfef74