Fix PixelTrackCleanerWrapper for quadruplet SeedingHitSet

PixelTrackCleanerWrapper assumed SeeingHitSets have 2 or 3 hits, resulting in pixel tracks that have 3 hits although they were reconstructed from quadruplets. Fixed by storing also the 4th hit if there is one.

Should not affect on pt/eta/etc of pixel tracks because the cleaning is done after the fit, but distributions sensitive to the number of hits may be affected.

FYI @thokc @cerati @rovere @VinInn