CHICAGO — More than a dozen Chicago aldermen on Thursday called on Mayor Brandon Johnson to scrap his 60-day shelter limit policy for migrants, the latest sign the City Council’s recent streak of independence has swelled with the city’s controversial responses to thehumanitarian crisis. Johnson allies such as Alds. Daniel La Spata and Byron Sigcho-Lopez are among the 16 aldermen who joined migrant response mutual aid groups in signing the letter to the mayor, along with more moderate council members like Ald. Matt O’Shea, 19th. Their protest comes on the heels of a bloc of 27 aldermen signing …