Remove FINAL_STATUS_HTML5_MEDIA and related messages.

They've been unused since r113742 when audio/video became deferred on
prerender. Also update a comment to account for media no longer being cancelled
that way.

Also remove some other dead code.

BUG=none
TEST=compiles, PrerenderBrowserTest.*

Review URL: https://chromiumcodereview.appspot.com/23484053

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224766 0039d316-1c4b-4281-b951-d872f2087c98
Disables DenyingMicDoesNotCauseStickyDenyForCameras on windows, its flaky

Test regularly times out.

R=xians@chromium.org
TBR=xians@chromium.org
BUG=295723

Review URL: https://codereview.chromium.org/24165004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224767 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224767