Removing ndsl.Namelist from PySHiELD

[jjuyeonkim]

Description
This follows from PyFV3 PR #88 and NDSL PR #246. It is part of NDSL Issue # 64.

This PR attempts to remove ndsl.Namelist from PySHiELD by doing the following:

• ModifiesPhysicsConfig.from_f90nml() to use only f90nml.Namelist via NDSL helper functions
• Removes PhysicsConfig.from_namelist()
• Modifies the translate tests to shed its reliance on ndsl.Namelist in favor the PhysicsConfig
• Adds --no_legacy_namelist to the github workflow translate.yaml

Partial work on NDSL Issue # 64

How Has This Been Tested?

• Existing unit tests

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 - There is a related Pace PR #153 that needs to be checked in first for the pace tests to pass.
• New check tests, if applicable, are included
• Targeted model if this changed was triggered by a model need/shortcoming

[romanc]

Looking good in my eyes. I left three optional comments inline.

[romanc]

🚀