Don't replace FloorDiv with floor in simplify, do simplifications for divisible exprs (#95076)
I don't see why `floor` is better than `FloorDiv` and solve with `FloorDiv` doesn't work anyway (the solution wouldn't be unique even if it worked).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/95076
Approved by: https://github.com/jansel, https://github.com/malfet, https://github.com/nkaretnikov
