Remove setCSSExclusionsEnabled(true) from CSS Shapes-Regions tests

Shapes are enabled by default when running tests, so the calls to internal settings can be removed.

Review URL: https://codereview.chromium.org/60013004

git-svn-id: svn://svn.chromium.org/blink/trunk@161412 bbb929c8-8fbe-4397-9dbb-9b2b20218538