gst-ffmpeg: drop .bbappend, moved to oe-core

* http://git.openembedded.org/openembedded-core/commit/?id=aab668fbba25d3e590e4182224b7b064d7705c5b
* you need to add orc to PACKAGECONFIG if you want to continue
  using it
* PRINC was dropped, oe-core commit had sufficient PR bump and
  this is going in almost simultaneously

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>