encx264: don't force-enable metrics (PSNR, SSIM).

Matches the x264 defaults, gives us a very minor speed boost, and gets rid of a warning.



git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5709 b64f7644-9d1e-0410-96f1-a4d463321fa5