Use new decay tree after substitutions (if they are done) in the DTF.

While the DTFDict allowed for substitutions in the decay tree to be made, when running the DTF it always used original particle and its decays. Effect of this was that when one does substitution to mass constrain to different particle, this was not actually done.

This fix should be also propagated to run2-patches for release for user analysis of run 1 and run 2 data.