San Francisco Muni Metro is moving to replace a train control system run by floppy disks.Santiago Mejia/The ChronicleSan Francisco transportation officials moved a step closer this past week to modernizing the train control system that runs the Muni Metro system, eventually ridding it of a system that uses outdated technology and runs on floppy disks.The Municipal Transportation Agency board on Tuesday approved a $212 million contract with Hitachi Rail for an up-to-date train control system that...