Removes the superblock variance contribution to the threshold
ntt-short1 results:
MEDIUM (%) HIGH (%)
PSNR 0.022148 -0.038920
PSNRHVS 0.047667 -0.053941
SSIM 0.014602 -0.046534
FASTSSIM -0.450261 -0.690958
Change-Id: Iaa8844d4d84c6265b488a4ade5a223bc3af99707