Johnson & Johnson plans to cut about 3,000 jobs, or 2.5 percent of its total workforce, from its medical devices business in a move that could set up the world's largest maker of health-care products to rebuild the unit through acquisitions. The company will reduce 4 to 6 percent of positions at the medical-device business over the next two years, leading to pretax restructuring costs of $2 billion to $2.4 billion.