Remove aria-pressed state from the captions button.
Remove aria-pressed state from the captions button.

Captions selection used to be a simple on/off button
and having aria-pressed state on it made sense. Now
that it's a gateway to text language selection the
state is no longer applicable.

Change-Id: I3780501afc8d3f5efa835ae9f015b44763c78c0e

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