Parse directly the Identifier instead of deducing it from the surface

Hi everbody,

I took a look into the crashes reported in ATLASRECTS-7774. For one reason or another, GlobalChi2Fitter creates PlaneSurfaces on-the-fly to propagate onto Mdt tubes. Interstingly, that's only happening in data... Anyhow, I parse now directly the Identifier of the mearuement through the different methods instead of taking it from the associatedSurface...... baaaad GlobalChi2Fitter.