Reference media-player-loader instead of media-player JS

This is already in static, so no need to duplicate the
jquery.player.min.js download.
Remove media-player JS file

The Nomensa media player is now included by static so we'll only be
explicitly including the media-player-loader file.
Remove the Nomensa media player library from frontend

This is now in static and is where we'll reference it from.
Merge pull request #250 from alphagov/remove-media-player-js

Remove media player js