Remove all of IDL attributes of Entity and Notation.

It should be safe because we don't provide any ways to get their objects.

Removing some virtual functions of Notation class makes it abstract. It is ok
because no one instantiates C++ Notation objects.

BUG=

Review URL: https://chromiumcodereview.appspot.com/23597034

git-svn-id: svn://svn.chromium.org/blink/trunk@157659 bbb929c8-8fbe-4397-9dbb-9b2b20218538