Use LocalMediaModel from LocalVideoView

Until now showing and hiding the video when the user enabled or disabled
it in the MediaControlsView required synchronizing both actions through
"app.setVideoEnabled". Now that MediaControlsView listens to the
LocalMediaModel calling that helper function can be replaced by direct
calls to the model.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>