ubuntu-cpc: only install shim-signed, run autoremove

The CPC build hooks for amd64 incorrectly attempt to install shim-signed
in addition to grub-efi-amd64 and grub-pc. These latter two packages
conflict with each other. Instead shim-signed should install whatever
packages are required.

Additionally, this will ensure that autoremove is run after installing
anything in the CPC build hooks. This is done to avoid shipping images
that include packages that are autoremovable. This will clean-up as
packages are installed and detect any breakage at build time.

live-build/ubuntu-cpc/hooks.d/base/disk-image-ppc64el.binary

@@ -33,6 +33,7 @@ install_grub() {
     chroot mountpoint apt-get -qqy update
     chroot mountpoint apt-get -qqy install grub-ieee1275
     chroot mountpoint apt-get -qqy remove --purge grub-legacy-ec2
+    chroot mountpoint apt-get autoremove --purge --assume-yes
 
     # set the kernel commandline to use hvc0
     mkdir -p mountpoint/etc/default/grub.d

live-build/ubuntu-cpc/hooks.d/base/disk-image-uefi.binary

@@ -89,11 +89,13 @@ install_grub() {
             efi_target=arm-efi
             ;;
         amd64)
-            chroot mountpoint apt-get install -qqy grub-efi-amd64-signed shim-signed
+            chroot mountpoint apt-get install -qqy shim-signed
             efi_target=x86_64-efi
             ;;
     esac
 
+    chroot mountpoint apt-get autoremove --purge --assume-yes
+
     chroot mountpoint grub-install "${loop_device}" \
         --boot-directory=/boot \
         --efi-directory=/boot/efi \

live-build/ubuntu-cpc/hooks.d/base/disk-image.binary

@@ -136,6 +136,7 @@ fi
 if [ "$ARCH" = "s390x" ]; then
     # Do ZIPL install bits
     chroot mountpoint apt-get -qqy install s390-tools sysconfig-hardware
+    chroot mountpoint apt-get autoremove --purge --assume-yes
 
     # Write out cloudy zipl.conf for future kernel updates
     cat << EOF > mountpoint/etc/zipl.conf

live-build/ubuntu-cpc/hooks.d/base/wsl.binary

@@ -35,6 +35,7 @@ cp -a rootfs.dir $rootfs_dir
 setup_mountpoint $rootfs_dir
 
 env DEBIAN_FRONTEND=noninteractive chroot $rootfs_dir apt-get -y -qq install ubuntu-wsl
+env DEBIAN_FRONTEND=noninteractive chroot $rootfs_dir apt-get autoremove --purge --assume-yes
 
 create_manifest $rootfs_dir livecd.ubuntu-cpc.wsl.rootfs.manifest
 teardown_mountpoint $rootfs_dir