Fixing bug where text track did not get cleaned up on video change.  This is not perfect since there is no equivalent API for removing a text track as there is for adding one.  You can remove all the cues from a track and disable the cc button but the cc button still exists since technically there is still a text track.  I tried parsing the DOM nodes to remove it but it is not there!… This must be a bug or gap in the API at this point.