BEIJING — Relatives shrieked and sobbed uncontrollably. Men and women nearly collapsed, held up by loved ones. Their grief came pouring out after 17 days of waiting for definitive word on the fate of the passengers and crew of the missing Malaysia Airlines jet. Malaysia’s prime minister gave that word late Monday in a televised announcement from Kuala Lumpur, saying there was no longer any doubt that Flight 370 went down in the southern Indian Ocean. Relatives of passengers in Beijing had been called to a hotel near the airport to hear the news, and some 50 of them gathered there. Afterward, they filed out of a conference room in heart-wrenching grief. One woman collapsed and fell on her…