MuonTruthAlgs: Fix memory leaks.
In MuonTruthDecorationAlg, firstPos and secondPos were not deleted on all possible code paths. Change them to use automatic allocation instead.
In MuonTrackTruthTool, not all code paths lead to where truthTrajectory is added to m_truthTrajectoriesToBeDeleted. Change to holding it via unique_ptr. I note that this class is also not thread-safe. This change does not attempt to fix that.