Clean up code-folding comments in assets.js
Clean up code-folding comments in assets.js

One of the ending comments seems to have gone away during a refactor.
This adds it back, and cleans up all the blocks with useful comments.

Change-Id: I29d093255805d806bb9957896ed348b0fdf8649e

shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player