Cleanup Blink's Platform from Screen Orientation stuff.

The embedders should now use WebScreenOrientationClient instead.

BUG=None

Review URL: https://codereview.chromium.org/339343003

git-svn-id: svn://svn.chromium.org/blink/trunk@176462 bbb929c8-8fbe-4397-9dbb-9b2b20218538