Fix thinning of HLTResult (ATR-18627)
The thinning was never applied to the old-style HLT::HLTResult as it
is stored as const in the event store. Fix this by const-cast. The
thinning of the xAOD::TrigNavigation worked as it's already non-const
in the store.
Besides fixing the bug, removed one templated method as we need different treatment for the const/non-const case.
For reference, this changes the trigger output in q431:
05-13 14:20 ERROR Py:diff-root INFO [HLT::HLTResult_p1_HLTResult_HLT]: 1622 leaves differ
05-13 14:20 ERROR Py:diff-root INFO [HLT::HLTResult_p1_HLTResult_HLT.m_navigationResult]: 40693 leaves differThis change was also validated in 21.0. For the moment, we don't want to add it there but the RunTier0Tests.log file is attached.