Fixing the z0 w.r.t PV calculation bug in PixeldEdxTrackParticleThinningTool

This request fixes the z0 w.r.t. PV calculation bug in PixeldEdxTrackParticleThinning.cxx used for DAOD_LLP1. The beam spot is missing in the current version. This changes the thinning efficiency for the low beta tracks(pT < 10 GeV). The impact is less than 0.1% for the file size. This tool was applied also to the pixel tracklet, but the pixel tracklets are kept by the other tool. The tool for tracklets is removed. discussion: https://indico.cern.ch/event/1501490/#sc-1-2-kek-waseda tag: @spagan