Only make tidal mixing files for meshes with cavities

[xylar]

Since the tidal model used to produce the dataset only covers the Southern Ocean, there is not much value in having the reampped dataset for meshes without cavities. If we want to make a more general mixing parameterization that uses tidal information, we would need to use data from a global tidal model for the input dataset in the future.

Checklist

• Document (in a comment titled Testing in this PR) any testing that was used to verify the changes

[xylar]

Testing

I ran remap_tidal_mixing from the generic file_for_e3sm test case using both the IcoswISC30E3r5 and IcosXISC30E3r7 meshes, with and without cavities, respectively. In the former case, the following files were produced, as expected:

map_S71W70_CATS_ustar_to_IcoswISC30E3r5_bilinear.nc
velocityTidalRMS_CATS2008_after_remap.nc
velocityTidalRMS_CATS2008.nc

In the latter case, no files were produced, as expected.

[xylar]

This addresses these comments from E3SM-Ocean-Discussion:
E3SM-Ocean-Discussion/E3SM#85 (comment)
E3SM-Ocean-Discussion/E3SM#85 (comment)
E3SM-Ocean-Discussion/E3SM#85 (comment)