Remove deprecated Gaudi/Chrono/ChronoIO.h

See !1707 (comment 9209159) and !1709 for details.

GaudiKernel/include/Gaudi/Chrono/ChronoIO.h

-/***********************************************************************************\
-* (c) Copyright 1998-2025 CERN for the benefit of the LHCb and ATLAS collaborations *
-*                                                                                   *
-* This software is distributed under the terms of the Apache version 2 licence,     *
-* copied verbatim in the file "LICENSE".                                            *
-*                                                                                   *
-* In applying this licence, CERN does not waive the privileges and immunities       *
-* granted to it by virtue of its status as an Intergovernmental Organization        *
-* or submit itself to any jurisdiction.                                             *
-\***********************************************************************************/
-#pragma once
-
-// empty file, kept for backward compatibility
-
-#include <chrono>
-#include <iostream>