Health-insurance companies could soon be forced to play by the same rules of free-market competition as everyone else. By an overwhelming majority, the House voted Wednesday to remove a 65-year-old antitrust exemption in order to put the brakes on sharply rising insurance costs. In California, Anthem Blue Cross customers are seeing an average rate increase of 25 percent. The vote came less than 24 hours before President Obama’s health-care summit, his latest effort to break the deadlock in Congress on his overhaul of the industry. The Senate’s version of the bill, though narrower in some ways, also strips medical malpractice insurers of the exemption. Obama has already said he would sign it into law.