Hello,
I think that the only solution is removing the Lun Masking, don't touch the Zonning!
If you remove the zone, the LUN3 will disappear too. You need to modify the lun masking in the Storage Device in order to only remove LUN1 y 2.
About the impact in the host... i don't know if is possible to do something in this scenario, your logs maybe will show you how the host is always looking for these Luns...
Regards