Move deletion of the QDrag object into QDragManager::drag().

The QDrag objects were apparently leaking on all platforms
other than XCB.

Task-number: QTBUG-39651
Change-Id: I09efcd250c1f42eb385e9d5779be7af6b9b59376
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>

src/gui/kernel/qdnd.cpp

@@ -142,6 +142,7 @@ Qt::DropAction QDragManager::drag(QDrag *o)
     QGuiApplicationPrivate::instance()->notifyDragStarted(o);
     const Qt::DropAction result = m_platformDrag->drag(m_object);
     m_object = 0;
+    o->deleteLater();
     return result;
 }
 

src/plugins/platforms/xcb/qxcbdrag.cpp

@@ -1010,9 +1010,6 @@ void QXcbDrag::handleFinished(const xcb_client_message_event_t *event)
 //            current_target = 0;
 //            current_proxy_target = 0;
 
-            if (t.drag)
-                t.drag->deleteLater();
-
 //            current_target = target;
 //            current_proxy_target = proxy_target;
 //            current_embedding_widget = embedding_widget;