Most Americans live in places where healthy people, including students in schools, can safely take a break from wearing masks under new U.S. guidelines released Friday. The Centers for Disease Control and Prevention outlined the new set of measures for communities where COVID-19 is easing its grip, with less of a focus on positive test results and more on what’s happening at hospitals. The new system greatly changes the look of the CDC’s risk map and puts more than 70% of the U.S. population in counties where the coronavirus is posing a low or medium threat to hospitals. Those are the people w…