removed use of BeginEvent incident
Removed use of BeginEvent for TagInfoMgr as required for multithreading running. And cleaned up a bit for old things no longer used. Documentation in class updated. Note that one does NOT need the BeginEvent - it was just the logical thing to do in the past. Proceeding on the BeingInputFile incident is sufficient, as the TagInfoMgr is called AFTER the IOVMetaDataTool which does the merging in the output metadata store.
Described in https://twiki.cern.ch/twiki/bin/view/AtlasComputing/InFileMetadataToMT And somewhat related to ATEAM-531