Adaptation of afe4a97d03, but we properly unlink the timesheet lines themselves instead of going for the account.analytic.lines like the original commit proposition did. Actually, the unlink method of hr.analytic.timesheet already unlinks the corresponding acount.analytic.line, but those records were previously deleted via ondelete='cascade', which didn't trigger the unlink method at all, so the associated analytic lines were not deleted accordingly.
Fixes opw 628256.
5f45e7ca96