Remove apt, debconf cruft files from /var/cache in all our livefses.

debian/changelog

@@ -2,6 +2,7 @@ livecd-rootfs (2.477) UNRELEASED; urgency=medium
 
   * Remove boot/grub leftovers from our root squashfs, left behind after
     grub purge.
+  * Remove apt, debconf cruft files from /var/cache in all our livefses.
 
  -- Steve Langasek <steve.langasek@ubuntu.com>  Fri, 13 Oct 2017 14:18:45 -0400
 

live-build/auto/build

@@ -210,6 +210,10 @@ EOF
 
 	lb chroot "$@"
 
+	# remove crufty files that shouldn't be left in an image
+	rm -f chroot/var/cache/debconf/*-old
+	Chroot chroot apt clean
+
 	if [ -f config/oem-config-preinstalled ]; then
 
 # This is cargo-culted almost verbatim (with some syntax changes for