Fix Low-Q2 tagger truth associations

[simonge]

#1589 broke the tagger truth associations.

This can either be fixed by making a CombinedTrackAssociations collection or moving the Tagger hits to a separate reconstruction pathway as suggested in #1571. Avoiding unnecessary attempts to match tracks to clusters and PID information and removing the (only possible) ID as an electron from the record.

The introduction of TaggerTrackerTrackAssociations should be done either way.