Fix name clash for TrigConf::HLTChain
The class was defined in TrigConfData/HLTChain and TrigConfHLTData/HLTChain. For now the new class was name TrigConf::Chain, but the plan is to remove TrigConfHLTData and change the new class to HLTChain
Addresses ATR-20088 and MR !25225 (closed)