I don't have a build environment were I can actually test it, but here's an attempt to update the debian/rules file so that (under Ubuntu) it generates a /usr/share/grub/default/grub file that uses "GRUB_TIMEOUT_STYLE=hidden" instead of a GRUB_HIDDEN_TIMEOUT= line.
(Note that grub-pc.config and grub-pc.postinst would also need to be updated to reflect this change.)
I don't have a build environment were I can actually test it, but here's an attempt to update the debian/rules file so that (under Ubuntu) it generates a /usr/share/ grub/default/ grub file that uses "GRUB_TIMEOUT_ STYLE=hidden" instead of a GRUB_HIDDEN_ TIMEOUT= line.
(Note that grub-pc.config and grub-pc.postinst would also need to be updated to reflect this change.)