Yes it's removable. But the aperture sight, being part of this rail, must be replaced with another sight.
This was a concern with my latest Marlin 1894, having this same rail. I don't care for it. I'll never use it, so my plan was to remove the rail and replace the sight. I never had ambition enough to make the change, so my little rifle still wears the rail, but now I don't even notice it's there.