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

src/generic/dragimgg.cpp

@@ -358,8 +358,7 @@ bool wxGenericDragImage::EndDrag()
 #else
         m_windowDC->DestroyClippingRegion();
 #endif
-        delete m_windowDC;
-        m_windowDC = NULL;
+        wxDELETE(m_windowDC);
     }
 
 #ifndef wxHAS_NATIVE_OVERLAY