WASHINGTON — The Supreme Court is hearing a case Wednesday that could make it easier for the president to fire the head of the agency that oversees government-controlled mortgage giants Fannie Mae and Freddie Mac.The case could also mean undoing an agreement between the companies and the government that has sent about $246 billion in their profits to the Treasury. That was compensation for the taxpayer bailout they received after the 2007 housing market crash.The case before the justices involves the Federal Housing …