dbcheck: Do not regard old one-way-links as errors

dbcheck: Do not regard old one-way-links as errors

Samba does not maintain one way links when the target is deleted or renamed
so do not fail dbcheck because of such links, but allow them to be updated.

This matters because administrators and make test expect that normal Samba
operation do NOT cause the database to become corrupt, and any error from
dbcheck tends to trigger alarms (or test failures).

If an object pointed at by a one way link is renamed or deleted in normal
operations (such as intersiteTopologyGenerator pointing at a demoted DC),
or make test, then this could trigger.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
BUG: https://bugzilla.samba.org/show_bug.cgi?id=12577