SAN FRANCISCO — Yahoo is trying to phase out passwords with an update to its mobile application for its e-mail service.The renovated app released Thursday for iPhones and Android devices will include an option called “Account Key” that allows people to sign into their e-mail accounts by pressing on a notification sent to their smartphones instead of typing in a password.Yahoo believes the new feature will be more secure because most people rely on passwords that are easy for hackers to guess. Yahoo&rsquo …