[Dashboard] Eliminate redundancy in AddPointHandler.post
[Dashboard] Eliminate redundancy in AddPointHandler.post

We were assigning the |data| field twice for no reason, which is a little
scary. We were also calling self.request.get twice for what is probably a
quite large field, so this probably eliminates an unnecessary copy as
well.

BUG=catapult:#3120

Review-Url: https://codereview.chromium.org/2615053003

benschmaus/catapult,benschmaus/catapult,sahiljain/catapult,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult,sahiljain/catapult,catapult-project/catapult,catapult-project/catapult-csm,benschmaus/catapult,catapult-project/catapult-csm,benschmaus/catapult,sahiljain/catapult,catapult-project/catapult-csm,benschmaus/catapult,benschmaus/catapult,catapult-project/catapult,benschmaus/catapult,sahiljain/catapult,catapult-project/catapult,sahiljain/catapult,sahiljain/catapult,catapult-project/catapult-csm