(Photo: Clive Barda) David Alden’s 2018 production of “Lohengrin,” Wagner’s hokey fable of love, fidelity, and politics, is receiving its first revival from Peter Relton at the Royal Opera House. Alden’s setting is generic postwar Europe, all bombed out windows and bare brick, with buildings at precariously jaunty angles (sets by Paul Steinberg). In the ruins of this world Konig {…}