Revert "Fix passing Unicode strings via wxIPC when using DDE"

This reverts commit c657fd3d61 because
changing the format of DDE advise requests/replies is not a good idea:
other applications (those using previous versions of wxWidgets or even
not using wxWidgets at all) may rely on getting data in real CF_TEXT
format rather than in one of text formats preceded by the extra byte
containing the actual format and the previous commit would have silently
broken this.

Another fix for #17900 will be implemented instead.

samples/ipc/server.cpp

@@ -268,11 +268,7 @@ void MyServer::Advise()
     {
         const wxDateTime now = wxDateTime::Now();
 
-        m_connection->Advise
-        (
-            m_connection->m_advise,
-            wxString::FromUTF8("\xd0\x9f\xd1\x80\xd0\xb8\xd0\xb2\xd0\xb5\xd1\x82")
-        );
+        m_connection->Advise(m_connection->m_advise, now.Format());
 
         const wxString s = now.FormatTime() + " " + now.FormatDate();
         m_connection->Advise(m_connection->m_advise, s.mb_str(), wxNO_LEN);