ctsm5.3.053: Fix and improve anomaly forcings for ISSP cases

[samsrabin]

Description of changes

Fixes a bug, and also makes it much simpler to run land-only SSP cases. Depends on ESCOMP/CDEPS#292.

Specific notes

Contributors other than yourself, if any: @ekluzek

CTSM Issues Fixed (include github issue #):

• Fixes SSP cases get rcp45 anomalies #2301
• Resolves Turn on anomaly forcing for ISSP compsets #922
• Resolves Example, user_nl_datm_streams file for anomaly forcing for NUOPC coupler #1730
• Helps with Docs: Remove refs to DATM_CLMNCEP_YR_* and DATM_CPL_YR_* variables #2743

Are answers expected to change (and if so in what way)? Yes, for cases that were being bitten by #2301 before.

Any User Interface Changes (namelist or namelist defaults changes)? Yes; see ESCOMP/CDEPS#292.

Does this create a need to change or add documentation? Did you do so? Yes; yes.

• Update docs

Testing performed, if any:

• Existing datm_rcp45_anom_forc test unaffected as of 4b96267.
• Existing datm_ssp126_anom_forc test unaffected as of c4ec313.

Remaining work after merging ctsm5.3.052:

• Run ssp test suite
• Run the three ctsm_sci tests that were failing.
• Handle the fact that those are still failing due to CDEPS not liking CRU-JRA
• In progress Run aux_clm test suite (with --skip-tests-with-existing-baselines)
• Fix aux_clm NEON tests (done with 21bb0dc) and rerun on both Derecho and Izumi

[ekluzek]

In ctsm5.3.050 these three ctsm_sci SSP tests fail:

SMS_Ld5.f09_t232.ISSP245Clm60BgcCropCrujra.derecho_intel.clm-ciso_dec2050Start	(SETUP)		
SMS_Ld5.f09_t232.ISSP370Clm60BgcCropCrujra.derecho_intel.clm-ciso_dec2050Start	(SETUP)		
SMS_Ld5.f09_t232.ISSP585Clm60BgcCropCrujra.derecho_intel.clm-ciso_dec2050Start	(SETUP)	

I'm marking this as the reason for it, as bringing this in will fix it.