[ATR-20747] fix in post-test testAthenaTrigAOD_TrigDecTool.py

We have already run the trigger by this point. Don't schedule the creation of trigger bits, it happened already in RDOtoRDOTrig

Note that testAthenaTrigAOD_TrigDecTool_fixedInput.py did not need fixing

This is a legacy test script which is still just about hanging on here with an MT setup.