[giow] (0) Drop the inert='' attribute since its use case is subsumed by <dialog>.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=24983
Affected topics: DOM APIs, HTML

git-svn-id: http://svn.whatwg.org/webapps@8536 340c8d12-0b0e-0410-8428-c7bf67bfef74