QNetworkInformation: remove redundant friend declaration

Q_DECLARE_PRIVATE already marks the Private as a friend of the Public
class. No need to do it manually.

Fixes GCC's -Wredundant-decls.

Amends 0875626e22.

Pick-to: 6.7 6.5
Task-number: QTBUG-115583
Change-Id: I26f8a42e375c1377c03fe60ccccadc5d0c3b02c5
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/network/kernel/qnetworkinformation.h

@@ -83,7 +83,6 @@ Q_SIGNALS:
 
 private:
     friend struct QNetworkInformationDeleter;
-    friend class QNetworkInformationPrivate;
     QNetworkInformation(QNetworkInformationBackend *backend);
     ~QNetworkInformation() override;