(umo,vmo)-z-space has different 2d mask from (umo,vmo)-native

[StephenGriffies]

There is a distinct 2d horizontal mask used for (umo,vmo)-z-space relative to (umo,vmo)-native. The mask for (umo,vmo)-z-space shows more ocean points than (umo,vmo)-native. So far as I can see, the extra unmasked points in (umo,vmo)-z-space have zero values. So the answers are the same for depth integrated transports. But the maps differ due to different masks.

We should make the masks the same to avoid confusion.