DETROIT — General Motors is cutting production of its all-electric BrightDrop delivery vans at a plant in Canada and will idle the facility through much of this year. The plant will be reduced from two shifts to one shift — eliminating 500 jobs — after being idled beginning next month for roughly 20 weeks until October. Battery pack assembly at the plant also will be down for two weeks before the prolonged shutdown. The Detroit automaker on Friday confirmed the plans for its CAMI assembly plant in Ontario and said the decisions are not related to President Donald Trump’s tariffs….