vp9: Switch to model=1 for skin detection.
vp9: Switch to model=1 for skin detection.

Very small change in speed (within 0.5%),
somewhat better detection over RTC clips.

Change-Id: I5bf0a7438fa7ccb60b26887125099e3238e5f298

mwgoldsmith/vpx,ShiftMediaProject/libvpx,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,mbebenita/aom,mwgoldsmith/libvpx,webmproject/libvpx,mwgoldsmith/libvpx,GrokImageCompression/aom,GrokImageCompression/aom,ittiamvpx/libvpx-1,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,webmproject/libvpx,luctrudeau/aom,webmproject/libvpx,ShiftMediaProject/libvpx,mbebenita/aom,mbebenita/aom,luctrudeau/aom,mbebenita/aom,smarter/aom,mbebenita/aom,mwgoldsmith/vpx,ittiamvpx/libvpx-1,Topopiccione/libvpx,mbebenita/aom,luctrudeau/aom,mwgoldsmith/vpx,mbebenita/aom,mwgoldsmith/vpx,Topopiccione/libvpx,Topopiccione/libvpx,mwgoldsmith/libvpx,ittiamvpx/libvpx-1,mwgoldsmith/vpx,smarter/aom,mwgoldsmith/libvpx,GrokImageCompression/aom,Topopiccione/libvpx,Topopiccione/libvpx,smarter/aom,webmproject/libvpx,webmproject/libvpx,ittiamvpx/libvpx-1,ShiftMediaProject/libvpx,mbebenita/aom,ittiamvpx/libvpx-1,luctrudeau/aom,smarter/aom,Topopiccione/libvpx,luctrudeau/aom,webmproject/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,mbebenita/aom,luctrudeau/aom,mwgoldsmith/vpx,smarter/aom,smarter/aom,ittiamvpx/libvpx-1