The delete right on account.bank.statement and account.bank.statement.line
was granted to a super user group via ir.model.access rows added in account_usability_misc
(ec22b72). We dropped the super user group when moving the protection feature to
this module (in the commit ebb39f5), without re-adding them, leaving perm_unlink stuck at 0 for
group_account_user until a full account module update.
Reset the unlink right for group_account_user in this commit, so the right is restored
automatically on install/upgrade of this module.
