TriggerJobOpts+TriggerTest: move flag defaults into ART tests

Cleanup flag settings in runHLT.py that were left from the early development stages:

• Remove Exec.MaxEvents, Concurrency.NumThreads and Trigger.doLVL1 and set them in the relevant ART tests.
• When running the trigger in athena, make RDO-writing the default to limit the number of flags that need to be specified (in ART tests). Note that running in athenaHLT, BS-writing is the default.