Remove duplicate media.js

Was identical to /common/media.js
Remove unused functions in media.js

Found to be unused by grepping for the function names, and verified by
running all tests including media.js manually and not finding any
regressions.
Rewrite relative paths to /common/media.js to absolute paths

This makes it easier to move tests and figure out where media.js is
when reading the tests.
Move media.js code used only by audio_003.htm into that test

audio_003.htm should clearly be rewritten using testharness.js,
but this branch is for media.js cleanup only.
Merge pull request #620 from foolip/cleanup-media-js

Cleanup of media.js