Remove MonGroup json filename from HLTJO db json file
As reported by @shanisch (ATR-24820) duplicate HLT JO files were created for the same menu, as the MonGroup json file name included the prescale set: "MonitoringJsonFileName": "HLTMonitoring_Dev_pp_run3_v1_22.0.55.json"
Replaced the value with "None" as for the other Json file names in the HLTJobOptions.db.json file