Yes, he runs the biggest asset management firm the world has ever seen. But right now, Laurence D. Fink has a little hedge-fund problem. Fink’s BlackRock Inc., the $4.5 trillion behemoth known for its mutual funds and ETFs, threw in the towel on its lackluster macro hedge fund last month -- a humbling capitulation that stunned the investing world. While hedge funds represent only a tiny fraction of BlackRock’s total assets...