Major bug in landice/antarctica/mesh_gen

[trhille]

When running the landice/antarctica/mesh_gen case using default config settings, the mesh that is created is unusable:

Thanks to @cwsmith for catching this!

[xylar]

Looks fine to me!

[trhille]

My initial thought was that that this was caused by the new cell culler, but the problem persists even when I checkout commit 51e65a5e342aa34bec97fb5478be7b75abc8be6e and use dev_compass_1.2.0-alpha.5. In the testing section of the mesh generation refactor PR, I reported that the mesh was identical to the code before the refactor. However, there are numerous clean-up commits after that testing that could be responsible for the issue. That points to insufficient testing on my part.

[trhille]

Further investigation reveals that antarctica_8km_2020_10_20_floodFillMask.nc contains only isolated pockets of ice, which indicates an issue with the flood fill.

[trhille]

Testing indicates that this was introduced by 8b327bd.

[xylar]

@trhille, very sorry about that! I don't understand why it's a problem but let's revert it!