Revert multimodel module to v2.2.0

[valeriupredoi]

Description

DO NOT MERGE JUST YET - I need to create a clone of current main so we don't lose the current MM module

Closes #1201

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[zklaus]

It's not decided to revert this module just yet.

[valeriupredoi]

It's not decided to revert this module just yet.

indeed, we need to reach a decision on this, I suggest we do it soon so we know which way we go 👍

[codecov]

Codecov Report

Merging #1202 (274305c) into main (3b653c4) will decrease coverage by 0.01%.
The diff coverage is 92.48%.

@@            Coverage Diff             @@
##             main    #1202      +/-   ##
==========================================
- Coverage   85.51%   85.50%   -0.02%     
==========================================
  Files         188      188              
  Lines        9147     9161      +14     
==========================================
+ Hits         7822     7833      +11     
- Misses       1325     1328       +3     

Impacted Files	Coverage Δ
esmvalcore/_recipe.py	91.10% <ø> (-0.02%)	⬇️
esmvalcore/_recipe_checks.py	81.98% <ø> (-0.23%)	⬇️
esmvalcore/preprocessor/_multimodel.py	92.70% <92.48%> (-1.41%)	⬇️

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[valeriupredoi]

heads up we should close this if no revert is decided to be needed @zklaus

[zklaus]

Cheers for the heads-up, V. I have it on the radar (now the milestone as well). Revert is still a possibility imho until the ancillary variables issue is resolved, so let's keep it open for now. Having it on the 2.3.1 milestone makes sure we don't just forget it.

[zklaus]

Issues dealt with elsewhere, see ESMValGroup/ESMValTool#2218.