Fixed usage of task_arena from tbb in HLTControlFlowMgr
This had been broken in the past for Allen, in order to work around the lack of nextEvent
in the IQueueingEventProcessor
interface.
Expect this was a pure mistake, nextEvent
has always been there. Allen now uses it and thus we can go back to proper code in HLTControlFlowMgr
Goes together with Allen!1592 (merged)