Fix comments in build_intra_predictors_high()
Fix comments in build_intra_predictors_high()

1. Removed TODOs, no longer applicable to finalized vp9 profiles.
2. Added explanation on assumed values for highbitdepth profiles.

Change-Id: I59e0bebaaab900cc611ed284daa5fa0bdedb8097

GrokImageCompression/aom,GrokImageCompression/aom,mwgoldsmith/libvpx,smarter/aom,GrokImageCompression/aom,GrokImageCompression/aom,mbebenita/aom,smarter/aom,mwgoldsmith/vpx,smarter/aom,luctrudeau/aom,mwgoldsmith/vpx,mbebenita/aom,webmproject/libvpx,mwgoldsmith/libvpx,webmproject/libvpx,Topopiccione/libvpx,mbebenita/aom,ShiftMediaProject/libvpx,mbebenita/aom,ShiftMediaProject/libvpx,smarter/aom,Topopiccione/libvpx,mwgoldsmith/vpx,mbebenita/aom,luctrudeau/aom,Topopiccione/libvpx,luctrudeau/aom,Topopiccione/libvpx,mbebenita/aom,Topopiccione/libvpx,mbebenita/aom,mbebenita/aom,GrokImageCompression/aom,webmproject/libvpx,Topopiccione/libvpx,webmproject/libvpx,mwgoldsmith/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,GrokImageCompression/aom,ShiftMediaProject/libvpx,smarter/aom,mwgoldsmith/vpx,luctrudeau/aom,smarter/aom,mbebenita/aom,mwgoldsmith/vpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,webmproject/libvpx,luctrudeau/aom,mwgoldsmith/libvpx,luctrudeau/aom,webmproject/libvpx