KiCad does not have customizable taskbars yet. KiCad’s development is quite amazing, but there is a limit to what the programmers can do in the available time.
If it really annoys you, you can probably remove it with a bit of hacking. I seem to recall that all icons are packed together in a zipped archive. If you can identify that file and remove the icon from it, then KiCad can’t show it, and the rest will probably still work.
Edit: Oops, I assumed no space would be reserved when the Icon was removed, but I trust that someone with a KiCad badge on his Avatar knows better than me.