Remove v8-private dependency from WebKit2.pri

Originally added in:
Commit:  962f67243db88bf43f149cc3989a40579401d168
Author:  Raine Makelainen <raine.makelainen@jollamobile.com>
Date:    (5 months ago) 2013-09-10 22:13:21 +0300
Subject: [qtwebkit] Add experimental header component