Disable broken Bitcodin HLS asset

The audio from this clip ends about 9 seconds early and so can't be
played to the end.  This asset was previously disabled without a
comment about why.  This now has a clear comment.

Change-Id: I63607837aa8a18928a778ccf4301c1b0510da376

demo/common/assets.js

@@ -693,6 +693,8 @@ shakaAssets.testAssets = [
       /* iconUri= */ 'https://storage.googleapis.com/shaka-asset-icons/sintel.png',
       /* manifestUri= */ 'https://bitdash-a.akamaihd.net/content/sintel/hls/playlist.m3u8',
       /* source= */ shakaAssets.Source.BITCODIN)
+      // Disabled because the audio playlist ends about 9 seconds early somehow.
+      .markAsDisabled()
       .addFeature(shakaAssets.Feature.HIGH_DEFINITION)
       .addFeature(shakaAssets.Feature.HLS)
       .addFeature(shakaAssets.Feature.MP2TS)