Disable xattrs in all mksquashfs calls

--chroot-squashfs-compression-options does not exist in live-build
bookworm (1:20230502). The correct mechanism is the MKSQUASHFS_OPTIONS
environment variable read by binary_rootfs.

Export MKSQUASHFS_OPTIONS="-no-xattrs" before lb build so live-build's
binary_rootfs picks it up, and add -no-xattrs explicitly to every
direct mksquashfs call in build.sh (fast-path repack and the dormant
split-layers function). Remove the invalid lb config option.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/build.sh

@@ -928,7 +928,7 @@ fast_path_repack_squashfs() {
     echo "=== fast-path: repacking squashfs ==="
     _sq_new="${_sq}.new"
     rm -f "$_sq_new"
-    mksquashfs "$_tmp" "$_sq_new" -comp zstd -b 1048576 -noappend -no-progress
+    mksquashfs "$_tmp" "$_sq_new" -comp zstd -b 1048576 -noappend -no-progress -no-xattrs
     mv "$_sq_new" "$_sq"
     rm -rf "$_tmp"
     echo "=== fast-path: squashfs repacked ($(du -sh "$_sq" | cut -f1)) ==="
@@ -992,15 +992,15 @@ split_live_squashfs_layers() {
     move_tree_to_layer "$tmp_root/root" "boot/firmware" "$tmp_fw/root"
 
     rm -f "$usr_sq" "$fw_sq"
-    mksquashfs "$tmp_root/root" "${base_sq}.new" -comp zstd -b 1048576 -noappend -no-progress >/dev/null
+    mksquashfs "$tmp_root/root" "${base_sq}.new" -comp zstd -b 1048576 -noappend -no-progress -no-xattrs >/dev/null
     mv "${base_sq}.new" "$base_sq"
 
     if dir_has_entries "$tmp_usr/root"; then
-        mksquashfs "$tmp_usr/root" "${usr_sq}.new" -comp zstd -b 1048576 -noappend -no-progress >/dev/null
+        mksquashfs "$tmp_usr/root" "${usr_sq}.new" -comp zstd -b 1048576 -noappend -no-progress -no-xattrs >/dev/null
         mv "${usr_sq}.new" "$usr_sq"
     fi
     if dir_has_entries "$tmp_fw/root"; then
-        mksquashfs "$tmp_fw/root" "${fw_sq}.new" -comp zstd -b 1048576 -noappend -no-progress >/dev/null
+        mksquashfs "$tmp_fw/root" "${fw_sq}.new" -comp zstd -b 1048576 -noappend -no-progress -no-xattrs >/dev/null
         mv "${fw_sq}.new" "$fw_sq"
     fi
 
@@ -1679,6 +1679,7 @@ cd "${LB_DIR}"
 run_step_sh "live-build clean" "80-lb-clean" "lb clean --all 2>&1 | tail -3"
 run_step_sh "live-build config" "81-lb-config" "lb config 2>&1 | tail -5"
 dump_memtest_debug "pre-build" "${LB_DIR}"
+export MKSQUASHFS_OPTIONS="-no-xattrs"
 run_step_sh "live-build build" "90-lb-build" "lb build 2>&1"
 echo "=== enforcing canonical bootloader assets ==="
 enforce_live_build_bootloader_assets "${LB_DIR}"