Though workers at the plant tried to keep it open with protests, the Stella D’Oro factory in The Bronx closed down yesterday — a day ahead of schedule. The workers went on strike last year, after Brynwood Partners, the private equity firm that had taken the plant over, kicked out the union; Brynwood locked them out and, when the plant was ordered to reinstate them by the National Labor Relations Board, announced they would close it down and move operations to Ohio instead. Workers showed a game face — “We showed we cannot be humiliated by them,” a 24-year veteran of the factory said. “We are not slaves.” — but it can’t be pleasant to lose all hope of returning to one’s job in a borough where unemployment is over 13 percent. The Kingsbridge facility had been running almost 80 years prior to closure.