Fix outlier removal in PrKalman
We get errors on the alignment because PrKalman removes too many outliers in the velo: the output contains tracks that have hits in too few stations. We can copy the logic from TrackMasterFitter so solve this:
- first select the LHCbIDs in the remaining nodes
- create HitPattern to count how many layers are on the track (this takes care of double nodes (VP x,y) and of multiple hits in the same layer)
- only remove a hit if the number of layers is larger than the minimum