Remove duplicated audio autoplay test

The version in ../media-elements/audio_003.htm is in better shape.
Remove redundant HTMLMediaElement IDL tests

All the attributes are covered by html/dom/interfaces.html
Remove duplicated video tests

The versions in ../media-elements/ are clearly derived from these tests,
and in some cases have improvements. (This was checked manually simply
by diffing files by the same name.)
Move video tests that are not HTMLVideoElement-specific

Most of these have companion audio tests already in ../media-elements/,
so there is some work to be done on merging those.
Remove manual video tests

020 is basically a duplicate of the video_initially_paused reftest.
021 is not possible to automate.
Merge pull request #625 from foolip/delete-move-media

Delete and move media tests