Is Maths, F. Maths, Bio and Chem a good combination? Watch
You could always drop FM after year 12 if you decide you are definitely going to apply to a course where it isn't necessary. However if your school structures their maths/FM teaching so you do all of A-level Maths and take the exam in year 12, then do all of FM an take the exam for that in year 13, you should contact universities you may wish to apply to in order to check whether this is acceptable as some may expect you to be taking a full set of 3 exams in year 13 (e.g. most medical schools and Oxbridge).
Physics isn't necessary for CS, mathematics, or any of those subjects that might overlap these (such as data science). While fundamentally computers are physical objects that function following physical laws, the "lower level" functioning of computers in that sense tends to be covered by electronic/computer engineering degrees, rather than computer science ones (where you typically cover an overview of computer architecture and so on but won't be learning the details of semiconductor physics).