Refactor mtj decorations
Use of this code was mostly in tests of other classes: e.g. AuxStoreInternal_test.cxx or ut_xaodrootaccess_tauxstore_test.cxx
Use of this code was mostly in tests of other classes: e.g. AuxStoreInternal_test.cxx or ut_xaodrootaccess_tauxstore_test.cxx