Revert "[CSS Shapes] clamp RasterShape shapeMargin to reference box size"

This reverts r258671 (commit 04d85dfa329176dc489bdcf9d2654f38e72a484e) as it broke android.

BUG=355167
TBR=pdr@chromium.org

Review URL: https://codereview.chromium.org/209303002

git-svn-id: svn://svn.chromium.org/blink/trunk@169771 bbb929c8-8fbe-4397-9dbb-9b2b20218538