landlock: Remove incorrect warning

landlock: Remove incorrect warning

landlock_put_hierarchy() can be called when an error occurs in
landlock_merge_ruleset() due to insufficient memory.  In this case, the
domain's audit details might not have been allocated yet, which would
cause landlock_free_hierarchy_details() to print a warning (but still
safely handle this case).

We could keep the WARN_ON_ONCE(!hierarchy) but it's not worth it for
this kind of function, so let's remove it entirely.

Cc: Paul Moore <paul@paul-moore.com>
Reported-by: syzbot+8bca99e91de7e060e4ea@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/20250331104709.897062-1-mic@digikod.net
Reviewed-by: Günther Noack <gnoack@google.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>