Use wxDELETE() and wxDELETEA() when possible.

Use wxDELETE[A]() functions which automatically NULL out their arguments after
deleting them instead of doing it manually.

Closes #9685.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64656 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/dragimag/dragimag.cpp

@@ -135,8 +135,7 @@ void MyCanvas::OnMouseEvent(wxMouseEvent& event)
 
         m_dragImage->Hide();
         m_dragImage->EndDrag();
-        delete m_dragImage;
-        m_dragImage = NULL;
+        wxDELETE(m_dragImage);
 
         m_draggedShape->SetShow(true);
 
@@ -203,8 +202,7 @@ void MyCanvas::OnMouseEvent(wxMouseEvent& event)
 
             if (!m_dragImage->BeginDrag(beginDragHotSpot, this, fullScreen))
             {
-                delete m_dragImage;
-                m_dragImage = (wxDragImage*) NULL;
+                wxDELETE(m_dragImage);
                 m_dragMode = TEST_DRAG_NONE;
 
             } else