Removing the -webkit prefix from CSS Regions-Shapes tests

Layout tests should use the new, unprefixed CSS Shapes properties.
The prefix has been removed for CSS Shapes in https://src.chromium.org/viewvc/blink?view=rev&revision=160750

Review URL: https://codereview.chromium.org/60873002

git-svn-id: svn://svn.chromium.org/blink/trunk@161407 bbb929c8-8fbe-4397-9dbb-9b2b20218538