Pare down 'BASE_SEED' handling to only those flavors which still use it.

Per the comments, BASE_SEED was initially used to identify the seed in the
flavor to use for identifying preseeded snaps, and later was also used to
identify which "minimal-remove" seed to apply to an image.

The first usage is now obsolete after a refactor; we now correctly detect
snaps from any of the included seeds without needing an explicit
declaration.

The second usage only applies to installer images that are NOT using layered
squashfs, since for these images 'minimal' is a separate squashfs layer
rather than a list of packages to remove after the fact.

Refactor this code to eliminate pointless definitions of BASE_SEED and
define it only for the subset of flavors today that:
 - have a 'minimal-remove' seed
 - are not using layered squashfs.

debian/changelog

@@ -1,3 +1,9 @@
+livecd-rootfs (24.04.39) UNRELEASED; urgency=medium
+
+  * Pare down 'BASE_SEED' handling to only those flavors which still use it.
+
+ -- Steve Langasek <steve.langasek@ubuntu.com>  Sun, 18 Feb 2024 10:27:50 -0800
+
 livecd-rootfs (24.04.38) noble; urgency=medium
 
   * Fix overlooked syntax error

live-build/auto/config

@@ -1209,29 +1209,10 @@ case $SUBPROJECT in
 		;;
 esac
 
-# we'll expand the base seed given here according to the STRUCTURE file, and
-# then look in all of the seeds found to see which snaps are seeded
-case $PROJECT:${SUBPROJECT:-} in
-	ubuntu-wsl:*)
-		BASE_SEED='wsl'
-		;;
-	ubuntu-cpc:*)
-		# we don't preseed any snaps in minimized images, so no need to set
-		# BASE_SEED in that case.
-		if [ "${SUBPROJECT:-}" != minimized ]; then
-			BASE_SEED='server'
-		fi
-		;;
-	ubuntu-server:live)
-		BASE_SEED='server'
-		;;
-	ubuntu-base:*|ubuntu-core:*|ubuntu-mini-iso:|ubuntu-oci:*|\
-        xubuntu:minimal)
-		;;
-        edubuntu:*)
-		BASE_SEED='desktop-gnome'
-		;;
-	*)
+case $PROJECT in
+	kubuntu|ubuntu-mate|ubuntu-unity|ubuntukylin)
+		# only used now for the 'minimal-remove' functionality,
+		# which is not used at all in layered images
 		BASE_SEED='desktop'
 		;;
 esac