This patch updates also the default cdfs for skip mode. It also remove
the unneeded checking on whether the best obtained RD mode aligned
with the skip mode.

For 30 frames, on both AWCY and Google lowres/midres test sets, with
the following config, the coding gain ranges from ~-0.15% to -0.23%:

--disable-ext-partition --disable-ext-partition-types --disable-txmg
--enable-jnt-comp --enable-mfmv

Change-Id: I39aeeb9e7b27ca679c1b3f9c0eea67b5e1f694e2