vp9-denoiser: Set motion threshold for skin_map to 0.

More aggresive on avoiding denoising on skin.
May supplement this later by adding condtion onn consec_zeromv.

Change-Id: Ied92b332f9b24e821d2009f81d1565758588d9a5

vp9/encoder/vp9_denoiser.c

@@ -212,7 +212,7 @@ static VP9_DENOISER_DECISION perform_motion_compensation(VP9_DENOISER *denoiser,
 
   saved_mbmi = *mbmi;
 
-  if (is_skin && motion_magnitude > 16)
+  if (is_skin && motion_magnitude > 0)
     return COPY_BLOCK;
 
   // If the best reference frame uses inter-prediction and there is enough of a