Disable allow_partition_search_skip feature
Disable allow_partition_search_skip feature

This feature was added to help speed up still images and slideshows.
It didn't work anymore, and thus was disabled. Code cleanup will
follow.

This had negligible impact to regular test sets. Borg test result
on ugc360p set at speed 3.
  avg_psnr:  ovr_psnr:  ssim:    speed:
   -0.244    -0.278    -0.153    -0.973

Change-Id: If74edabce0c93be1361e645ffd2eec063c2db76b

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