I have also uninstalled bash4 and gdb, so that I have 36 Mb free on rootfs before upgrade.
But the upgrade process by "apt-get upgrade" still complains with "no space left on device"... after fixing with "dpkg --configure -a" and another "apt-get upgrade" it succeeded with only 3 Mb free on rootfs.

After reboot and some days, rootfs is now 38 Mb free. Strange, it looks like the upgrade requires a lot of temporary space that gets freed only with cron tasks.

My suspect is /var/lib/dpkg which was 44 Mb after the first upgrade failure and is now 16 Mb large.