This option increases runtime by 20% and is only marginally
better than good cpu-used=0:

   PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
-0.3382 | -0.3911 | -0.4875 |  -0.2982 | -0.2992 | -0.3164 |    -0.3686

It is also not well integrated with speed_features.c, which is
the main reason for the removal.

Change-Id: If88c50367f63b860ad57f650869b978ec7734aad