The `\! -path "${DESTDIR}/usr/lib/debug/boot/*"` part effectively made DEBUG_DIRS always be limited to /usr/lib/debug/boot directory only, which is not correct, since there may be nested directories inside boot/, like kernel/, kernel/gdb, modules/, and thus these would not be deleted during `make delete-old`, which also will prevent the boot/ itself from being deleted, since rmdir(1) won't remove non-empty directory.
Fixes: 63cd05d97a6d ("remove debug files in delete-old* when WITHOUT_DEBUG_FILES")