LArConditionsCommon_comm_jobOptions: Remove LArFlatConditionsSvc (now all done by cond-algos)
As far as I know, all clients of LAr Electronic Calibration have now be migrated to CondHandles that read from the ConditionStore. This MR stops scheduling the legacy LArFlatConditionsSvc that populates DetectorStore with the same information.
Saves some 30 MBytes of vmem.
Note: This affects only real-data processing, not MC!