vp9: remove condition on high bitdepth using simple block yrd.
vp9: remove condition on high bitdepth using simple block yrd.

Speed is similar between non HBD vs 8bit with HBD build.

BUG=webm:1541

Change-Id: I8b5f7eff87ec7dc4710d31744155a60e50b0f0a9

webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx