When the original port of LeptonTaggers was completed from r21 (!66768 (merged)), the function
mergeIteratively2TrackVtxs was removed from execution because of memory management problems. This MR fixes the memory management in
mergeIteratively2TrackVtxs and restores it in execution. This should be the last major piece of LeptonTaggers that needs to be restored for now.
This MR should only be merged after !67642 (merged). I'm making this a new MR because I anticipate that the fixes will be somewhat involved, and I want to make review easy for the shifters.