'CGAffineTransformIdentity' is unavailable in Swift
Found this link which suggested that "The global constant was moved into a static property, and the Swift 3 migrator, as you've discovered, failed to correct for that. " and that you can simply change the code to :
toView.transform = CGAffineTransform.identity
EDIT
or even simpler:
toView.transform = .identity
Hope this helps somebody.