update-initramfs missing /lib/modules/4.4.0-13-generic
Solution 1:
The utility update-initramfs looks in var/lib/initramfs-tools. You will find an entry for that old kernel there. Removing it:
sudo rm /var/lib/initramfs-tools/4.4.0-13-generic
will get rid of that error
(the locale issue is something else entirely...)