Improve selection in Charm_D0ToHHHH_BuilderD0ToKmPimPipPip_untight"

The following discussion from !3142 (merged) should be addressed:

• @cacochat started a discussion: (+1 comment)

  @gunther or @yitang could we proceed by merging this?

added selection label

assigned to @cacochat

added Charm hlt2 labels