ONDON, May 14 — Britain will become the first country in the world to sell a cholesterol-reducing drug, called a statin, without a prescription. Starting in July, a low dosage of the drug Zocor will be sold over the counter to people at moderate risk of heart disease, a number that could reach 5 million to 10 million. That group includes all men older than 55, as well as men over 45 and women over 55 who smoke, are overweight, have a family history of heart disease or come from the Indian subcontinent, all groups that are at higher risk...