Fidelity Investments’ Abigail Johnson was scheduled to take center stage on Tuesday, as she counsels money managers gathering in Washington about charting their future in the digital world. But the chief executive, a featured speaker at one of the industry’s biggest conferences, will also be struggling with a stubborn legacy of the past: the treatment of women in the world of finance. Over the last two months, Fidelity, one of the largest investment companies, has dismissed two portfolio managers -- one over allegations of inappropriate sexual comments and another over claims of sexually harassing a female junior employee.