bugfix SOM cellpool

[flohump]

🐦 Purpose of this PR 🐦

• the model was infeasible with cfg$gms$c56_emis_policy <- "sdp_soil" and cfg$gms$som <- "cellpool_aug16"
• the reason for this was a missing equation in 59_som/cellpool_aug16 for the dimension actualNoAcEst in vm_carbon_stock. Therefore, this dimension was a free varialbe, causing the infeasiblity.
• the missing equation has been added
• the unused dimensions previousLandPattern and previousCarbonDensity in vm_carbon_stock have been removed in all parts of the model
• No entry in changelog needed. Bugfix of unpublished code.

🔧 Checklist for PR creator 🔧

• Labeling pull request correctly from the label list.

• Low risk : Simple bugfixes (missing files, updated documentation, typos) or Start/output scripts
• Medium risk : New realization / Changes to existing realization / Other changes which don't modify default.cfg
• High risk : New input files (if cfg$input is changed in default.cfg) / Modification to core model (eg. changes in equations, calculations, introduction of new sets etc.) / Other changes in default.cfg

• Providing additional information based on PR label

• Low risk : No new model run needed.
• Medium risk : Default run based on the current version of the fork from which PR is made
• High risk
  • Default run from the current develop branch: PR402_curDev_SSP2-Ref
  • Default run based on the current version of the fork from which PR is made: PR402_thisPR_SSP2-Ref

• 📉 Performance loss/gain from current default behavior 📈
  • Current develop branch default : 0.47 h
  • This PR's default : 0.39 h

Runs with CO2 price

• Added changes to CHANGELOG.md
• Compilation check (model starts without compilation errors - use gams main.gms action=c in model folder for testing).
• No hard coded numbers and cluster/country/region names.
• The new code doesn't contain declared but unused parameters or variables.
• Where relevant, In-code comments added including documentation comments.
• Made sure that documentation created with goxygen is okay (use goxygen::goxygen() for testing).
• Changes to magpie4 R library for post processing of model output (ideally backward compatible).
• Self-review of my own code.
• For high risk runs: validation of major model indicators - Land-use, emissions, food prices, Tau. %Delete this line in case it is not a high risk run%

⚠️ Additional notes or warnings ⚠️

NA

🚨 Checklist for RSE reviewer 🚨

• PR is labeled correctly.
• CHANGELOG is updated correctly
• No hard coded numbers and cluster/country/region names.
• No unnecessary increase in module interfaces
• All required updates in interfaces (if any) have been properly adressed in the module contracts
• In-code comments and documentation comments are satisfactory.
• model behavior/performance is satisfactory.
• Requested changes (if any) were applied correctly

🚨 Checklist for MAgPIE reviewer 🚨

• PR is labeled correctly.
• CHANGELOG is updated correctly
• No hard coded numbers and cluster/country/region names.
• Changes to the model are scientifically sound
• In-code comments and documentation comments are satisfactory.
• model behavior/performance is satisfactory.
• Requested changes (if any) were applied correctly

[FelicitasBeier]

For as far as I can judge, it looks fine.
I would suggest Kristine as 59_som expert to also have a quick look, though, as well.
Just to make sure that previousLandPattern and previousCarbonDensity are indeed no longer required?

[k4rst3ns]

This makes all sense to me and resolve the problem with the unbound variable.