Bug#996596: [linux-image-amd64] dkms error on kernel image removal

[Lyndon Brown <jnqnfe@gmail.com>]

Package: linux-image-amd64
Version: 5.14.12-1

I tried to purge linux-image-5.14.0-1-amd64 yesterday and ran into an
error. I additionally tried to purge linux-image-5.14.0-2-amd64 today
following the release of linux-image-5.14.0-3-amd64 and ran into the
same error, which I've copied below.

Please can you advise how to clean up after the failure, is removal of
the old '/lib/modules/5.14.0-x-amd64' directories and their contents
sufficient?

$ sudo dpkg --purge linux-image-5.14.0-2-amd64
(Reading database ... 274461 files and directories currently installed.)
Removing linux-image-5.14.0-2-amd64 (5.14.9-2) ...
/etc/kernel/prerm.d/dkms:
dkms: removing:   (5.14.0-2-amd64) (x86_64)
Error! Arguments <module> and <module-version> are not specified.
Usage: remove <module>/<module-version> or
       remove -m <module>/<module-version> or
       remove -m <module> -v <module-version>
I: /vmlinuz.old is now a symlink to boot/vmlinuz-5.14.0-3-amd64
I: /initrd.img.old is now a symlink to boot/initrd.img-5.14.0-3-amd64
/etc/kernel/postrm.d/initramfs-tools:
update-initramfs: Deleting /boot/initrd.img-5.14.0-2-amd64
/etc/kernel/postrm.d/zz-update-grub:
Generating grub configuration file ...
Found background image: /usr/share/images/desktop-base/desktop-grub.png
Found linux image: /boot/vmlinuz-5.14.0-3-amd64
Found initrd image: /boot/initrd.img-5.14.0-3-amd64
Adding boot menu entry for EFI firmware configuration
done
Purging configuration files for linux-image-5.14.0-2-amd64 (5.14.9-2) ...
rmdir: failed to remove '/lib/modules/5.14.0-2-amd64': Directory not empty
dpkg: warning: while removing linux-image-5.14.0-2-amd64, directory '/lib/modules/5.14.0-2-amd64' not empty so not removed