Remove support for nemsio

[WalterKolczynski-NOAA]

Description
For a while global-workflow was supporting both the legacy nemsio filetype as well as NetCDF. There is no longer any need to support the older filetype, and UFS doesn't even support it anymore.

Requirements
Remove any code branches that depend on $OUTPUT_FILE, keeping only the code relevant for netcdf.
Any variables that are no longer needed should be removed, and any variables that no longer change should be replaced with their static value.

Acceptance Criteria (Definition of Done)
No code relevant only to nemsio remains.

Dependencies
None