MAIDUGURI, Nigeria — A suicide bombing in the northeast Nigerian town of Biu killed about 19 people and injured 17, a day before the president made a visit to another town in another state hit by violence. The bodies and remains of about 20 people were brought to the hospital in the town in Borno state after Wednesday’s attack, said Nasiru Buhari, a member of the Civilian Joint Task Force, formed by residents to fight against the militant group Boko Haram. Nigerian defense officials have announced recent victories in the fight against the insurgents, claiming to have recaptured towns across the embattled northeast, where Boko Haram’s insurgency has displaced an estimated 1.6 million. The U.S.