xAODTrigEgammaAthenaPool+xAODTrigRingerAthenaPool: Add missing dummy files.

Add some missing dummy converter files, so that cmake will realize that we have custom converters in this package.

Event/xAOD/xAODTrigEgammaAthenaPool/src/xAODElectronTrigAuxContainerCnv.cxx

+/*
+  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
+*/
+
+// Dummy file so that cmake will know this is a custom converter.
+//  xAODElectronTrigAuxContainerCnv.h