By Josh Horwitz SHANGHAI (Reuters) -Boston Celtics highlights were absent from China’s Tencent Holdings Ltd sports platform after their backup center Enes Kanter criticized Chinese President Xi Jinping and China’s treatment of Tibet. Kanter, who has a history of activism speaking out against his native Turkey’s President Tayyip Erdogan, tweeted a two-minute video of himself expressing support for Tibet and wearing a T-shirt emblazoned with the image of the Dalai Lama, its exiled spiritual leader. “I’m here to add my voice and speak out about what is happening in Tibet. Under the Chinese govern…