Britain’s only two pandas will soon be returned to China, officials said, in a send-off that has dispirited fans of the playful, waddling bears and signals what appears to be the end, at least for now, of panda diplomacy. “Bamboo bon voyage,” the Edinburgh Zoo of the Royal Zoological Society of Scotland said on its website, noting that there would be “a giant farewell” on Thursday for the bears, whose names are Yang Guang and Tian Tian. The pair of giant pandas will be prepared to return to China in…