Remove some cases for turning off arf.
Flipping arf on and off too often is hurting some clips. This change makes no difference for 50-75% of our test clips but helps some by a big margin. (eg. std-hd crew by 6% and one of the YT and YT-hd clips by 14%) Average improvements for 2 pass, speed 2 (psnr,ssim) are as follows:- derf 0.165%, 0.210% yt 1.210%, 1.464% yt-hd 1.189%, 1.471% std-hd 1.031%, 0.886% Change-Id: I121fe66cfb4a62d384b23b484a7d648789641969