Remove velo, ST, OT

Removing obsolete detectors. See https://gitlab.cern.ch/lhcb-dpa/project/-/issues/37

Changes:

• Vis/SoEvent : as much as possible, velo -> VP, ST -> UT, OT -> FT. Some functionality seems missing. See PK-R3C tags in code.

Loosely depends on LHCb!2804 (merged) (would likely build without it but better merged at the same time).