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/msw/window.cpp

@@ -3987,8 +3987,7 @@ bool wxWindowMSW::HandleDestroy()
     {
         m_dropTarget->Revoke(m_hWnd);
 
-        delete m_dropTarget;
-        m_dropTarget = NULL;
+        wxDELETE(m_dropTarget);
     }
 #endif // wxUSE_DRAG_AND_DROP