Starter. The extra protein won't hurt them. I'm sure of that. Not as sure about the extra calcium in Layer not hurting them.
The studies that I have seen that show that the extra calcium raises mortality rates and damages internal organs in chicks start off with the Layer being the only feed with day old chicks. I have not seen any studies that shows what happens if you feed it to older chicks. The older they are, the less likely it is to do damage. Since I don't know when the danger age is passed, I don't feed chicks Layer until after they start to lay. Why make life complicated when you can make it simple?