CSP 1.1: Remove the 'SecurityPolicy' interface.

We're dropping the script interface from CSP 1.1 until we can get it right.
Aligning Blink with that decision.

This should have zero web-visible effect, as the feature is still locked
behind the experimental web features flag.

Thread: http://lists.w3.org/Archives/Public/public-webappsec/2014Jan/0001.html
Change: https://github.com/w3c/webappsec/commit/18882953ce2d8afca25f685557fef0e0471b2c9a

BUG=335489

Review URL: https://codereview.chromium.org/132613003

git-svn-id: svn://svn.chromium.org/blink/trunk@165317 bbb929c8-8fbe-4397-9dbb-9b2b20218538