Fix lingering references to shakaExtern
Fix lingering references to shakaExtern

We renamed the extern namespace, but these references were in comments
that were not examined by the compiler.

Change-Id: If232953f678fba703c5355445f4f0cf180b46749

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