Unify cfsr and gefs datm datamodes

[NickSzapiro-NOAA]

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Description of changes

Code for cfsr and gefs datm datamodes is very similar (just with different function names). This PR removes the duplicates. As gefs datm datamode is already in ESCOMP/CDEPS, gefs is retained here. Note that GFS, GEFS, CFSR, etc. input datasets are still handled via streams in the same way, just with datamode == 'GEFS'.

Specific notes

Contributors other than yourself, if any:

CDEPS Issues Fixed (include github issue #): https://github.com/NOAA-EMC/CDEPS/issues/64

Are there dependencies on other component PRs (if so list):

Are changes expected to change answers (bfb, different to roundoff, more substantial): bfb

Any User Interface Changes (namelist or namelist defaults changes): Remove cfsr datm datamodes. Use gefs instead

Testing performed (e.g. aux_cdeps, CESM prealpha, etc): UFS regression test suite

Hashes used for testing: See https://github.com/ufs-community/ufs-weather-model/pull/2389