Changed PrResidualSeeding to a template to possibly run it on Downstream tracks
Currently PrResidualSeeding only removes the tracks that were used in PrForward or PrMatch. With this templating, we can also remove tracks extended to form Downstream tracks, and so only save (if wanted) pure T tracks
Related to LHCb!3212 (merged) and Moore!988 (merged)
Edited by Louis Henry