Biogen will stop selling its Alzheimer’s treatment Aduhelm, a drug once seen as a potential blockbuster that stumbled after its launch a few years ago. The company also is helping Japanese drugmaker Eisai sell another Alzheimer’s treatment, Leqembi, which received full FDA approval last summer. When Aduhelm debuted in 2021, it was the first new Alzheimer’s drug in nearly two …