amd64: always install grub-pc with shim-signed

shim-signed depends on grub-efi-amd64-signed, which in turn has
alternative depends on either `grub-efi-amd64 | grub-pc`. However to
support booting with either via shim&signed-grub and BIOS, the choice
must be made to install grub-pc, not grub-efi-amd64.

This makes images consistent with Ubuntu Deskop, Live Server, buildd
bootable images; all of which already do install grub-pc and
shim-signed.

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.

LP: #1901906

live-build/auto/config

@@ -775,8 +775,7 @@ case $PROJECT in
 				add_package install grub-pc
 				;;
 			amd64)
-				add_package install grub-pc-bin
-				add_package install grub-efi-amd64-signed
+				add_package install grub-pc
 				add_package install shim-signed
 				;;
 		esac

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

@@ -97,11 +97,13 @@ 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 grub-pc shim-signed
             efi_target=x86_64-efi
             ;;
     esac
 
+    chroot mountpoint apt-get autoremove --purge --assume-yes
+
     # This call to rewrite the debian package manifest is added here to capture
     # grub-efi packages that otherwise would not make it into the base
     # manifest. filesystem.packages is moved into place via symlinking to

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