Follow-up from "Cleanup State::Location implementation"

The following discussion from !4370 (closed) should be addressed:

• @gunther started a discussion: (+5 comments)

  Unfortunately, there's also https://gitlab.cern.ch/lhcb/LHCb/-/blob/master/Event/TrackEvent/include/Event/Track_v3.h#L40 do you think this can be unified? 😄