By Aaron Keebaugh Lithe and economical, Boston Baroque’s superb production of Iphigénie en Tauride proved the old adage that less can be more. Iphigénie en Tauride, an opera in four acts. Libretto by Nicolas-François Guillard. Music by Christoph Willibald Gluck. Performed by Boston Baroque. Martin Pearlman, conductor. Mo Zhou, stage director. At GBH’s Calderwood Studio,…