you can find this setting now in the "LANDESK Antivirus Action Center". Navigate to "Agent Settings" and click the little gear. and select the "LANDESK Antivirus Action Center". The first option there is "Acknowledge that other antivirus software will be removed". The box should be checked there.
Thanks Cristian, I went to the action center but looks like the box is already checked in there.
If you check this list,
it says Windows 8 Defender is not removable. But for older ones it should work. Maybe in the meantime it is supported but thats the newest list I could find in the community.
Hope it helps
All these systems affected are Windows 7 32-bit so it looks like it should be disabled.