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/gtk/clipbrd.cpp

@@ -485,11 +485,7 @@ GdkAtom wxClipboard::GTKGetClipboardAtom() const
 void wxClipboard::GTKClearData(Kind kind)
 {
     wxDataObject *&data = Data(kind);
-    if ( data )
-    {
-        delete data;
-        data = NULL;
-    }
+    wxDELETE(data);
 }
 
 bool wxClipboard::SetSelectionOwner(bool set)