Remove/Comment the use of the high-threshold bit in PrLongLivedTracking

Remove/Comment the use of the high-threshold bit in PrLongLivedTracking. Small drop in efficiency, as the value in the MVA has to be set constant. Preparation for removal of highThreshold member in UTHit. The discrimination power of the highThreshold bit in terms of good tracks vs fake tracks is very small (on simulation) (in VeloUT there was no change in 100 events, in PrLongLivedTracking it was < 1%, but there it is an input to a NN), but a removal would make the UTHits slimmer, which could speed up the sequence. If it turns out to be very different in newer simulation, it can easily be reintroduced again.