Revert of initramfs package removal in KVM image (LP: #1880170)

It was reported and confirmed in LP bug #1875400
(https://bugs.launchpad.net/cloud-images/+bug/1875400) that on the public
KVM cloud image there exists a large list of packages marked for auto-removal.

This should never be the case on a released cloud image.

These packages are marked for auto-removal because in the KVM image binary hook
we removed both initramfs-tools and busybox-initramfs packages. Due to package
dependencies this also removed:

busybox-initramfs* cloud-initramfs-copymods* cloud-initramfs-dyn-netconf*
cryptsetup-initramfs* initramfs-tools* initramfs-tools-core* multipath-tools*
overlayroot* sg3-utils-udev* ubuntu-server*

But it did not remove all the packages that the above list depended on.
This resulted in all those packages being marked for auto-removal because they
were not manually installed nor did they have any manually installed packages
that depended on them.

The removal of initramfs-tools and busybox-initramfs was to avoid the
generation of initramfs in images that should boot initramfsless.

This requirement is obsolete now because the initramfsless boot handling
is now handled via setting GRUB_FORCE_PARTUUID in /etc/default/grub.d/40-force-partuuid.cfg.

In test images I have verified that GRUB_FORCE_PARTUUID is set and that
boot speeds have not regressed.

LP: #1880170

debian/changelog

@@ -1,3 +1,9 @@
+livecd-rootfs (2.620.3) eoan; urgency=medium
+
+  * Revert of initramfs package removal in KVM image (LP: #1880170)
+
+ -- Phil Roche <phil.roche@canonical.com>  Fri, 22 May 2020 13:03:20 +0100
+
 livecd-rootfs (2.620.2) eoan; urgency=medium
 
   * Fix logic to ensure snapd is seeded in core18-only images (LP: #1871919)

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

@@ -49,10 +49,6 @@ replace_kernel ${mount_d} "linux-kvm"
 chroot "${mount_d}" update-grub
 undivert_grub "${mount_d}"
 
-# Remove initramfs for kvm image
-env DEBIAN_FRONTEND=noninteractive chroot "${mount_d}" apt-get \
-    purge -y initramfs-tools busybox-initramfs
-
 env DEBIAN_FRONTEND=noninteractive chroot "${mount_d}" rm \
     -rf /boot/initrd.img-* /boot/initrd.img