fix red photoreceptor

[duerrsimon]

Rod photoreceptor cells do not have telodendria so the rod illustration is not correct. The same error was also found from Biorender, and they fixed it upon my request a few years ago. I am sad to see so many scientist in my field are using such illustration without knowing a real morphology of their research object. Also I concern those illustration did not go through a review process by morphology specialists.