Mods needed to run CAM4 F-compset (AMIP) configurations (ESCOMP#437)

Tag name (The PR title should also include the tag name):
atmos_phys0_28_001
Originator(s): nusbaume  (Claude Opus 5 helped find the issues).

Description (include issue title and the keyword ['closes', 'fixes',
'resolves'] and issue number):

Added some code modifications needed for the CAM4 + BAM
physics/chemistry suite to run stably in an F-compset (i.e. AMIP or
prescribed SSTs/sea ice) configuration.

List all namelist files that were added or changed:

M       schemes/rrtmgp/rrtmgp_constituents_namelist.xml
- Removed aquaplanet flag when setting radiatively active gases (which
should eventually be managed by the chemistry scheme anyways, see ESCOMP#435).

List all files eliminated and why: N/A

List all files added and what they do: N/A

List all existing files that have been modified, and describe the
changes:
(Helpful git command: `git diff --name-status
main...<your_branch_name>`)

M       schemes/rasch_kristjansson/rk_stratiform.F90
- Add fixer for negative surface precipitation, which matches what is
done in CAM.

List all automated tests that failed, as well as an explanation for why
they weren't fixed:

Is this an answer-changing PR? If so, is it a new physics package,
algorithm change, tuning change, etc?

Yes, the RK precipitation adjustment results in answer differences.

If yes to the above question, describe how this code was validated with
the new/modified features:

I did a five year run and looked at the results.

Author: nusbaume

schemes/rasch_kristjansson/rk_stratiform.F90

@@ -5,7 +5,6 @@ module rk_stratiform
 
   implicit none
   private
-  save
 
   ! public CCPP-compliant subroutines
   !   note: cloud_fraction_perturbation_run calls the compute_cloud_fraction
@@ -460,6 +459,15 @@ subroutine rk_stratiform_prognostic_cloud_water_tendencies_run( &
    prec_str(:ncol) = prec_str(:ncol) + prec_pcw(:ncol)
    snow_str(:ncol) = snow_str(:ncol) + snow_pcw(:ncol)
 
+   ! RK can occassionally produce negative precipitation fluxes, so force
+   ! it to be greater than or equal to zero.  Also ensure that snow is not
+   ! greater than the total precipitation. This is a non-physical adjustment,
+   ! but is the same technique that the original CAM4 model used:
+   do i = 1, ncol
+      if (prec_str(i) < 0._kind_phys) prec_str(i) = 0._kind_phys
+      if (snow_str(i) > prec_str(i))  snow_str(i) = prec_str(i)
+   end do
+
   end subroutine rk_stratiform_prognostic_cloud_water_tendencies_run
 
   ! Save Q, T, cloud water at end of stratiform microphysics for use in next timestep

schemes/rrtmgp/rrtmgp_constituents_namelist.xml

@@ -95,7 +95,7 @@
         'N:CFC11STAR:CFC11',
         'A:CFC12:CFC12'
       </value>
-      <value aquaplanet="1" phys_suite="cam4">
+      <value phys_suite="cam4">
         'N:O2:O2',
         'N:CO2:CO2',
         'N:ozone:O3',