Certainly do the GCSEs and work hard in those subjects. If you do those A levels you will find the ATPL exams easier, but only do them if you enjoy the subjects or think you will do better in them than others.
If you are going to be a pilot then education will help you develope as a person, help you learn to study and to work with focus, and I hope give you enjoyment. They also provide a back-up career whan needed! The actually subjects studied are not terribly important to your aviation career, unless there is a training scheme that requires certain A levels (perhaps others could say if there is; having done sciences myself I cannot recall if any courses actually required them).
I feel old. I already had a PPL and both those A levels when you were born.