First, Serena Williams. And now Roger Federer. The tennis world is having to say goodbye to another legend of the sport as the Swiss superstar took to social media to announce that he is retiring. “The Laver Cup next week in London will be my final ATP event,” Federer, 41, said in his statement. “I will play more tennis in the future, of course, but just not in Grand Slams or on the tour.” Federer, who debuted in 1997, retires with 20 Grand Slam singles titles, including eight wins at Wimbledon. He finishes his remarkable career behind Rafael Nadal (22) and Novak Djokovic (21) in major champio…