Remove unused and unnecessary margin code from RenderTable and RenderDeprecatedFlexibleBox.

Found this while working to move margin collapse code to RenderBlockFlow.

Review URL: https://chromiumcodereview.appspot.com/23526040

git-svn-id: svn://svn.chromium.org/blink/trunk@157731 bbb929c8-8fbe-4397-9dbb-9b2b20218538