They are the elite among the elite at Goldman Sachs, highfliers who are the envy of Wall Street. But on Washington’s orders, Goldman is now considering a step that once would have been unthinkable: disbanding the corps of market wizards at the heart of its lucrative trading operation. Under the new Dodd-Frank financial regulations, Goldman must break up its principal strategies group, the wildly successful trading unit that has helped power the bank’s profits.