Remove extra unaligned loop from alphablender.  Both aligned and unaligned loops were the same, so remove the extra.
BUG=none
TESTED=try bots.
R=brucedawson@google.com, harryjin@google.com

Review URL: https://webrtc-codereview.appspot.com/29059004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1166 16f28f9a-4ce2-e073-06de-1de4eb20be90