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
1 file changed