lib/dbus/ReadIter: remove obsolete GCC warning workaround

src/lib/dbus/ReadIter.hxx

 /*
- * Copyright 2007-2017 Content Management AG
+ * Copyright 2007-2020 CM4all GmbH
  * All rights reserved.
  *
  * author: Max Kellermann <mk@cm4all.com>
@@ -34,15 +34,8 @@
 #define ODBUS_READ_ITER_HXX
 
 #include "Iter.hxx"
-#include "util/Compiler.h"
 #include "util/ConstBuffer.hxx"
 
-#if GCC_OLDER_THAN(8,0)
-/* switch off completely bogus shadow warnings in older GCC
-   versions */
-#pragma GCC diagnostic ignored "-Wshadow"
-#endif
-
 namespace ODBus {
 
 class ReadMessageIter : public MessageIter {