KABUL — Afghan President Hamid Karzai’s cousin, Hashmat Khalil Karzai, was killed at his residence by a suicide bomber on Tuesday in Afghanistan’s southern Kandahar province, officials said. The bomber, a 16-year-old boy, detonated explosives hidden in his turban while embracing Hashmat Karzai as part of special greetings for the Eid al-Fitr Muslim holiday at Karzai’s home in Karz district of Kandahar, they said.