What type of sub-floor is suitable for laminate flooring?
The 1/4" plywood is likely luan. It's used to level the floor, often for a vinyl floor. For a hardwood floor, the main reason to have luan is shore up the floor and reduce any pitting or other slope issues. Whether you can remove the luan depends on the quality of your subfloor. If it has any imperfections, I would keep (or replace) the luan.