Remove unused QPicture::detach_helper() private method.

QPicture doesn't need this for quite a long time now, so get rid of it.

Change-Id: Ie575f32555deb130f7b27e11a7617fb2b3dc4e43
Reviewed-by: Marius Storm-Olsen <marius.storm-olsen@nokia.com>

src/gui/image/qpicture.cpp

@@ -1008,17 +1008,6 @@ int QPicture::metric(PaintDeviceMetric m) const
 \internal
 */
 
-/*! \internal
-### Qt 5 - remove me
- */
-void QPicture::detach_helper()
-{
-    // QExplicitelySharedDataPointer takes care of cloning using
-    // QPicturePrivate's copy constructor. Do not call detach_helper() anymore
-    // and remove in Qt 5, please.
-    Q_ASSERT_X(false, "QPicture::detach_helper()", "Do not call this function");
-}
-
 /*!
     Assigns picture \a p to this picture and returns a reference to
     this picture.

src/gui/image/qpicture.h

@@ -107,7 +107,6 @@ protected:
 
 private:
     bool exec(QPainter *p, QDataStream &ds, int i);
-    void detach_helper();
 
     QExplicitlySharedDataPointer<QPicturePrivate> d_ptr;
     friend class QPicturePaintEngine;