Source: grub Version: 0.97-72 Tags: buster sid Control: block 848163 by -1 I intend to remove the ncurses multilib packages after the stretch release, see #848163. I'm not quite sure how long you want to keep the grub-legacy package alive, but this means that you will at least have to build /usr/sbin/grub without ncurses support on amd64.
Simply dropping lib32ncurses5 from Build-Depends would be sufficient, and I guess most users never run the grub shell interactively from the running system anyway, but maybe it would also be good to have a NEWS.Debian mentioning how to install the i386 version of grub-legacy via multiarch if a full-fledged grub shell is desired for some reason.