CVE-2020-25720 s4:dsdb/descriptor: explain lack of dSHeuristics check

It is strange that sDRightsEffective pays no attention to the
dSHeuristics flags.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14810



Reviewed-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Signed-off-by: Andrew Bartlett <abartlet@samba.org>

Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Fri Sep 16 03:31:42 UTC 2022 on sn-devel-184