Remove 1.3 MB of superfluous media files for LayoutTests

These were unused or use where another file works just as well.

Note that test.webm was corrupted (encrypted?) so if it were ever
chosen by findMediaFile() it wouldn't work.

Also remove unused formats from media-file.js.

Review URL: https://codereview.chromium.org/603943002

git-svn-id: svn://svn.chromium.org/blink/trunk@182681 bbb929c8-8fbe-4397-9dbb-9b2b20218538