Non-rd mode: Limit transform size for intra to 16x16.
Non-rd mode: Limit transform size for intra to 16x16.

Limit transform size for intra to 16x16, for non-screen content mode.
Little/no change in speed or metrics.
32x32 intra block is rarley selected in RTC (non-screen content) case,
but some visual improvement can be seen in some example,
e.g., captured_video_dark_whd.yuv.

Change-Id: I68e2db87875343b3fb9bb407a7709f0088f84072

luctrudeau/aom,ShiftMediaProject/libvpx,ittiamvpx/libvpx-1,Topopiccione/libvpx,luctrudeau/aom,ittiamvpx/libvpx-1,Topopiccione/libvpx,thdav/aom,jmvalin/aom,mwgoldsmith/vpx,ShiftMediaProject/libvpx,openpeer/libvpx_new,openpeer/libvpx_new,shacklettbp/aom,luctrudeau/aom,ShiftMediaProject/libvpx,mbebenita/aom,openpeer/libvpx_new,mwgoldsmith/libvpx,GrokImageCompression/aom,GrokImageCompression/aom,webmproject/libvpx,mbebenita/aom,ittiamvpx/libvpx-1,mbebenita/aom,webmproject/libvpx,shacklettbp/aom,smarter/aom,openpeer/libvpx_new,jmvalin/aom,mwgoldsmith/vpx,luctrudeau/aom,shacklettbp/aom,mwgoldsmith/vpx,mwgoldsmith/vpx,Topopiccione/libvpx,webmproject/libvpx,mwgoldsmith/vpx,ShiftMediaProject/libvpx,GrokImageCompression/aom,openpeer/libvpx_new,mbebenita/aom,mbebenita/aom,jmvalin/aom,mbebenita/aom,openpeer/libvpx_new,ShiftMediaProject/libvpx,webmproject/libvpx,smarter/aom,thdav/aom,smarter/aom,mwgoldsmith/libvpx,thdav/aom,webmproject/libvpx,jmvalin/aom,thdav/aom,thdav/aom,shacklettbp/aom,Topopiccione/libvpx,jmvalin/aom,thdav/aom,shacklettbp/aom,shacklettbp/aom,mwgoldsmith/libvpx,Topopiccione/libvpx,ittiamvpx/libvpx-1,Topopiccione/libvpx,smarter/aom,jmvalin/aom,mwgoldsmith/libvpx,luctrudeau/aom,mwgoldsmith/libvpx,GrokImageCompression/aom,webmproject/libvpx,mbebenita/aom,mwgoldsmith/vpx,GrokImageCompression/aom,luctrudeau/aom,GrokImageCompression/aom,smarter/aom,ittiamvpx/libvpx-1,mwgoldsmith/libvpx,mbebenita/aom,ittiamvpx/libvpx-1,smarter/aom,mbebenita/aom