Hong Kong (AFP) – Books written by prominent Hong Kong democracy activists have started to disappear from the city’s libraries, online records show, days after Beijing imposed a draconian national security law on the finance hub.Among the authors whose titles are no longer available are Joshua Wong, one of the city’s most prominent young activists, and Tanya Chan, a well known pro-democracy lawmaker.Beijing’s new national security law was imposed on Tuesday and is the most radical shift in how the semi-autonomous city is run since it was handed back to China by Britain in 1997.China’s authorit…