Getting rid of a CLANG compilation warning.

CookieJar::deleteCookie hides overload virtual function
QNetworkCookieJar::deleteCookie.

The 2 methods have 2 different signatures, so all still
works, but CLANG throws an annoying warning at compile time.

This gets rid of that.
Fixing crash when assigning “page.cookieJar”.

As suggested by @Vitallium