Use the classic gadget for raspi images

debian/changelog

@@ -1,3 +1,10 @@
+livecd-rootfs (2.664.39) UNRELEASED; urgency=medium
+
+  * Switch to building raspi classic images using the 'classic' branch instead
+    of '18'. This is needed for proper Pi Zero 2 support (LP: #1960950).
+
+ -- Łukasz 'sil2100' Zemczak <lukasz.zemczak@ubuntu.com>  Tue, 15 Feb 2022 18:59:05 +0100
+
 livecd-rootfs (2.664.38) focal; urgency=medium
 
   * Add sleep due to e2fsck error in umount_partition. LP: #1960537

live-build/auto/config

@@ -429,18 +429,13 @@ case $IMAGEFORMAT in
 			# classic images
 
 			# Certain models have different names but are built from the same source gadget tree
-			BRANCH=18
+			BRANCH=classic
 			case $MODEL in
 				pi-arm64|pi3-arm64)
 					MODEL=pi
-					BRANCH=18-arm64
-					;;
-				pi)
-					BRANCH=18-armhf
 					;;
 				intel-iot)
 					MODEL=pc
-					BRANCH=classic
 					;;
 			esac