Remove all references to the "base" project, which has not been built since 16.04 release day.

debian/changelog

@@ -1,9 +1,14 @@
 livecd-rootfs (2.723) UNRELEASED; urgency=medium
 
+  [ Steve Langasek ]
   * Drop code for the 'ubuntu-core' project when not using
     image_format: ubuntu-image, as this is obsolete and not used to build
     core* snaps in recent series.
 
+  [ Michael Hudson-Doyle ]
+  * Remove all references to the "base" project, which has not been
+    built since 16.04 release day.
+
  -- Steve Langasek <steve.langasek@ubuntu.com>  Tue, 11 May 2021 17:08:24 -0700
 
 livecd-rootfs (2.722) impish; urgency=medium

debian/tests/default-bootstraps

@@ -13,7 +13,6 @@ fi
 # Listed subprojects can be combined with other projects as well,
 # but this list gives reasonable coverage.
 ALL_TRIPLETS="
- base::
  edubuntu::
  edubuntu-dvd::
  kubuntu::

live-build/auto/config

@@ -525,7 +525,7 @@ if [ "$PREINSTALLED" = "true" ]; then
 		ubuntu-server)
 			add_package live oem-config-debconf ubiquity-frontend-debconf
 			;;
-		ubuntu-base|ubuntu-oci|base|ubuntu-cpc)
+		ubuntu-base|ubuntu-oci|ubuntu-cpc)
 			;;
 		ubuntu)
 			add_package live oem-config-gtk ubiquity-frontend-gtk
@@ -732,10 +732,6 @@ case $PROJECT in
 		COMPONENTS='main restricted universe'
 		;;
 
-	base)
-		add_task install minimal standard
-		;;
-
 	ubuntu-server)
 		add_task install minimal
 		case ${SUBPROJECT:-} in
@@ -1000,7 +996,7 @@ if [ "${IMAGE_HAS_HARDCODED_PASSWORD:-}" = "1" ]; then
 fi
 
 case $PROJECT in
-  ubuntu-cpc|ubuntu-core|ubuntu-base|ubuntu-oci|base)
+  ubuntu-cpc|ubuntu-core|ubuntu-base|ubuntu-oci)
     # ubuntu-cpc gets this added in 025-create-groups.chroot, and we do
     # not want this group in projects that are effectively just chroots
     ;;