Catalysis of the reactions: (2R,3S)-2,4',7-trihydroxyisoflavanone = daidzein + H+ + H2O, and 2-hydroxy-2,3-dihydrogenistein = genistein + H+ + H2O.
2,7,4\'-trihydroxyisoflavanone hydro-lyase (daidzein-forming) activity