[ttml2] Remove dangling issue notes that have been resolved.

skynavga has just created a new issue for https://github.com/w3c/ttml2:

== Remove dangling issue notes that have been resolved. ==
Review and remove any dangling ``<issue>...</issue>`` elements.

Please view or discuss this issue at https://github.com/w3c/ttml2/issues/660 using your GitHub account

Received on Monday, 12 February 2018 20:05:20 UTC