LONDON — Boris Johnson wants a haircut and a beer. Like millions of other Britons, the prime minister will be able to have a trim and a tipple on Saturday, when the country takes its biggest step yet out of lockdown with the reopening in England of restaurants, pubs and hairdressers, along with secular and sacred venues including cinemas and churches. Britain is also opening up to travel, announcing Friday that it will scrap a requirement for people arriving from dozens of countries to spend 14 days in isolation.