QtGui: Clean up event headers

- Remove unimplemented  QSinglePointEvent()
- Remove forward declaration of QTouchEventTouchPointPrivate
- Update copyright and add comment to qevent_ph.h

Task-number: QTBUG-72173
Change-Id: Ie64b6071f2611001dcd8e3deec2f5ed382bb2312
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/gui/kernel/qevent.h

@@ -216,7 +216,6 @@ public:
 class Q_GUI_EXPORT QSinglePointEvent : public QPointerEvent
 {
 public:
-    QSinglePointEvent();
     QSinglePointEvent(Type type, const QPointingDevice *dev, const QPointF &localPos,
                       const QPointF &scenePos, const QPointF &globalPos,
                       Qt::MouseButton button = Qt::NoButton, Qt::MouseButtons buttons = Qt::NoButton,
@@ -928,7 +927,6 @@ inline bool operator==(QKeyEvent *e, QKeySequence::StandardKey key){return (e ?
 inline bool operator==(QKeySequence::StandardKey key, QKeyEvent *e){return (e ? e->matches(key) : false);}
 #endif // QT_CONFIG(shortcut)
 
-class QTouchEventTouchPointPrivate;
 class Q_GUI_EXPORT QTouchEvent : public QPointerEvent
 {
 public:

src/gui/kernel/qevent_p.h

@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2020 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtGui module of the Qt Toolkit.
@@ -40,6 +40,17 @@
 #ifndef QEVENT_P_H
 #define QEVENT_P_H
 
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API. It exists for the convenience
+// of other Qt classes. This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
 #include <QtGui/private/qtguiglobal_p.h>
 #include <QtCore/qurl.h>
 #include <QtGui/qevent.h>