Clean idct 8x8 neon functions
Clean idct 8x8 neon functions

BUG=webm:1301

Change-Id: I05f47dca1fddc155c8396e627cfccf6449677307

mwgoldsmith/vpx,webmproject/libvpx,mwgoldsmith/vpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,mwgoldsmith/vpx,mwgoldsmith/vpx,webmproject/libvpx,mwgoldsmith/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,mwgoldsmith/libvpx,mwgoldsmith/libvpx,mwgoldsmith/libvpx,mwgoldsmith/vpx,ShiftMediaProject/libvpx