Simplify deleteOwnedPtr() and deleteOwnedArrayPtr() functions

We can just use COMPILE_ASSERT to verify type's completeness.

Review URL: https://chromiumcodereview.appspot.com/23757036

git-svn-id: svn://svn.chromium.org/blink/trunk@157704 bbb929c8-8fbe-4397-9dbb-9b2b20218538