Remove forward declaration of non existing class

QUnixEventDispatcherQPA has no private class, there is no need to
declare a fake one.

Change-Id: I615304709fbbea83f6747bb6202dbfd2cc03256d
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/platformsupport/eventdispatchers/qunixeventdispatcher_qpa_p.h

@@ -56,12 +56,9 @@
 
 QT_BEGIN_NAMESPACE
 
-class QUnixEventDispatcherQPAPrivate;
-
 class QUnixEventDispatcherQPA : public QEventDispatcherUNIX
 {
     Q_OBJECT
-    Q_DECLARE_PRIVATE(QUnixEventDispatcherQPA)
 
 public:
     explicit QUnixEventDispatcherQPA(QObject *parent = 0);