Я не могу удалить старый образ ядра - Ubuntu 16.04.6 LTS

Мой uname -a возвращает следующее.

Linux <hidden> 4.4.0-116-generic #140-Ubuntu SMP Mon Feb 12 21:23:04 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

Когда я пытаюсь обновить пакеты, происходит сбой, показывая следующие ошибки, касающиеся старого ядра.

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following packages will be REMOVED:
  linux-image-3.13.0-68-generic linux-image-extra-3.13.0-68-generic
The following packages have been kept back:
  libapache2-mod-php libapache2-mod-php7.0 libgd3 php-gd php-mbstring php-mysql php-xml php7.0-cli php7.0-common php7.0-curl php7.0-dev php7.0-fpm php7.0-gd
  php7.0-json php7.0-mbstring php7.0-mcrypt php7.0-mysql php7.0-opcache php7.0-readline php7.0-soap php7.0-tidy php7.0-xml php7.0-xmlrpc php7.0-zip
0 upgraded, 0 newly installed, 2 to remove and 24 not upgraded.
4 not fully installed or removed.
After this operation, 194 MB disk space will be freed.
Do you want to continue? [Y/n] Y
(Reading database ... 142623 files and directories currently installed.)
Removing linux-image-extra-3.13.0-68-generic (3.13.0-68.111) ...
depmod: FATAL: could not load /boot/System.map-3.13.0-68-generic: No such file or directory
run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 3.13.0-68-generic /boot/vmlinuz-3.13.0-68-generic
run-parts: executing /etc/kernel/postinst.d/initramfs-tools 3.13.0-68-generic /boot/vmlinuz-3.13.0-68-generic
update-initramfs: Generating /boot/initrd.img-3.13.0-68-generic
WARNING: missing /lib/modules/3.13.0-68-generic
Ensure all necessary drivers are built into the linux image!
depmod: ERROR: could not open directory /lib/modules/3.13.0-68-generic: No such file or directory
depmod: FATAL: could not search modules: No such file or directory
E: amd64-microcode: unsupported kernel version!
depmod: WARNING: could not open /var/tmp/mkinitramfs_30aiDQ/lib/modules/3.13.0-68-generic/modules.order: No such file or directory
depmod: WARNING: could not open /var/tmp/mkinitramfs_30aiDQ/lib/modules/3.13.0-68-generic/modules.builtin: No such file or directory
run-parts: executing /etc/kernel/postinst.d/unattended-upgrades 3.13.0-68-generic /boot/vmlinuz-3.13.0-68-generic
run-parts: executing /etc/kernel/postinst.d/update-notifier 3.13.0-68-generic /boot/vmlinuz-3.13.0-68-generic
run-parts: executing /etc/kernel/postinst.d/x-grub-legacy-ec2 3.13.0-68-generic /boot/vmlinuz-3.13.0-68-generic
Searching for GRUB installation directory ... found: /boot/grub
Searching for default file ... found: /boot/grub/default
Testing for an existing GRUB menu.lst file ... found: /boot/grub/menu.lst
Searching for splash image ... none found, skipping ...
Found kernel: /boot/memtest86+.bin
dpkg-query: error: package 'grub-legacy-ec2' is not installed
run-parts: /etc/kernel/postinst.d/x-grub-legacy-ec2 exited with return code 10
dpkg: error processing package linux-image-extra-3.13.0-68-generic (--remove):
 subprocess installed post-removal script returned error exit status 1
Removing linux-image-3.13.0-68-generic (3.13.0-68.111) ...
Examining /etc/kernel/postrm.d .
run-parts: executing /etc/kernel/postrm.d/initramfs-tools 3.13.0-68-generic /boot/vmlinuz-3.13.0-68-generic
update-initramfs: Deleting /boot/initrd.img-3.13.0-68-generic
run-parts: executing /etc/kernel/postrm.d/x-grub-legacy-ec2 3.13.0-68-generic /boot/vmlinuz-3.13.0-68-generic
Searching for GRUB installation directory ... found: /boot/grub
Searching for default file ... found: /boot/grub/default
Testing for an existing GRUB menu.lst file ... found: /boot/grub/menu.lst
Searching for splash image ... none found, skipping ...
Found kernel: /boot/memtest86+.bin
dpkg-query: error: package 'grub-legacy-ec2' is not installed
run-parts: /etc/kernel/postrm.d/x-grub-legacy-ec2 exited with return code 10
Failed to process /etc/kernel/postrm.d at /var/lib/dpkg/info/linux-image-3.13.0-68-generic.postrm line 328.
dpkg: error processing package linux-image-3.13.0-68-generic (--remove):
 subprocess installed post-removal script returned error exit status 1
Errors were encountered while processing:
 linux-image-extra-3.13.0-68-generic
 linux-image-3.13.0-68-generic
E: Sub-process /usr/bin/dpkg returned an error code (1)

Редактировать: Вывод apt list --installed | grep grub

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

grub-common/xenial-updates,now 2.02~beta2-36ubuntu3.22 amd64 [installed]
grub-gfxpayload-lists/xenial,now 0.7 amd64 [installed,automatic]
grub-pc/xenial-updates,now 2.02~beta2-36ubuntu3.22 amd64 [installed]
grub-pc-bin/xenial-updates,now 2.02~beta2-36ubuntu3.22 amd64 [installed,automatic]
grub2-common/xenial-updates,now 2.02~beta2-36ubuntu3.22 amd64 [installed,automatic]