TrigMonitoring+AthenaMonitoring: delete obsolete MonitCategory modules
Delete the obsolete "MonitCategory" modules and the HLTMonTriggerList.
This feature is replaced by getHLTMonitoringAccess. Egamma remains
for the moment as it is used directly in a few places.
Also remove the now obsolete TriggerTranslatorSimple from AthMonitorAlgorithm (it's still used in the legacy ManagedMonitorToolBase but given we don't support legacy trigger monitoring anymore it will probably deleted entirely in a separate MR).