Backport v2022 <- v2023: Drop apertis delta switching the build-deps from libidn2 to libicu

libidn2 was wrongly considered as GPL-3, but actually the lib is GPL-2+ or LGPL-3+. Thus, our delta is not required.

Moreover, libpsl is used on the Apertis rootfs, but the switch to libicu pulled the huge libicu67. So, switching back to libidn2 will help to reduce the rootfs size.