That is controlled by the OS -- it's not really specific to calibre.
You'll see the same hand icon in the browser, when hovering over a link.
You can, however, change your cursor theme -- a rough guide is here:
https://askubuntu.com/questions/3000...-mouse-pointer
If the hand pointer bothers you in calibre, I assume it will bother you in other applications as well. It would be a good idea to change it universally.