this was made a no-op in:
01d23109 vp9: make VPX_CODEC_USE_FRAME_THREADING a no-op

and the test hitting this branch has been disabled since:
6ab0870d disable VP9MultiThreadedFrameParallel tests

rename the test to VP9MultiThreaded to exercise the tile-based threading

BUG=webm:1395

Change-Id: I35564a75eb5a7d7f7ccb923133b1b07295201f4c