The online classified advertising site Backpage.com abruptly shut its “adult” section on Monday, yielding to a campaign by state and federal government officials to close a service they contend promotes prostitution and human trafficking. The unexpected move came hours after a U.S. Senate subcommittee released a report accusing Backpage of actively editing posts on the site to remove evidence of child sex trafficking. In announcing its decision, Backpage said it was the victim of government censorship.