Remove handles to ROBDataProvider from HltEventLoopMgr
The code was a leftover from the migration from release 21. The handles were not actually used for anything in the current HltEventLoopMgr. The functionality which needed ROBDataProvider in HltEventLoopMgr in release 21 is now implemented by TrigByteStreamInputSvc. Moreover, the ITrigROBDataProviderSvc interface is not used online at all.
cc @wiedenma