LONDON—So, this is it. After 47 years of membership, Britain is finally leaving the European Union on Friday. It may have taken 1,316 days of screaming at each other since the referendum, and claimed the careers of two prime ministers, but at 11 p.m. the 17 million people who voted for Brexit three years ago will, for better or worse, get what they asked for.Now, given that all through the 2016 campaign, pro-Brexit campaigners spent their time casting the EU as a sinister, overreaching superstate that had shackled Britain’s potential for decades, you might assume that tonight’s historic strike of the clock would spark wild celebrations. Millions draped in Union Jacks, screaming Rule Britannia, and weeping warm, joyous tears into their even warmer pints of thick beige ale.But, despite the best efforts of some of the most wild-eyed foot-soldiers of the Brexit campaign, tonight’s landmark will pass without any great fanfare. If you voted to remain, there’s obviously nothing to celebrate. ...