Bug fixes and data_override logic updates

[bensonr]

Description
Fixes a bug in SHiELD/atmos_model for variable initialization.
In solo/atmos_model:

• updates module use handling
• removes outdated logic for data_override_init handling
• gives calendar an initial value

DEPENDENCY ON FMS PR #933

Fixes # (issue)

How Has This Been Tested?
This has been tested in FV3 solo tests to ensure proper handling of data_override_init with no grid_spec and an empty data_table. The variable initialization bug in SHiELD has been tested in a SHiELD run.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included

[laurenchilutti]

Will this work in Regional runs? Do we need an if bounded domain?

[bensonr]

@laurenchilutti - it might still be needed if someone does actually try to use data_override with a bounded domain independent of the existence of the grid_spec. I'll add it back in for the appropriate function calls.

[bensonr]

After looking at this further, this is for the solo runs and I don't think we'll be using any data_overrides in this system. Maybe it makes sense to go with the original and not include data_override_init.