remove outdated selection

[muell149]

@matz-e, is there a reason we require an available track to attach/run the selection on the taus[1]? It seems that we could run this independently. Also, I get sync'd up with thomas when removing the requirement in [1]. If you are OK with removing this, I'll just update the code, or submit a PR. Let me know what you think.

[1] https://github.com/cms-ttH/ttH-LeptonID/blob/master/plugins/LeptonIdentifier.cc#L728-Lundefined