TrigT1CaloCalibTools+TrigT1CaloCalibToolInterfaces: Migrate to VarHandle.

Migrate L1CaloTriggerTowerDecoratorAlg/L1CaloxAODOfflineTriggerTowerTools to use Read/WriteHandle. Make tool private.

IL1CaloxAODOfflineTriggerTowerTools::initDatabase is never called, and the concrete implementation is problematic for MT. Remove it.