Remove usage of updatestep when calculating projection

[dafeda]

Its cleaner and requires less work to use ensemble_config directly.

Pre review checklist

• Read through the code changes carefully after finishing work
• Make sure tests pass locally (after every commit!)
• Prepare changes in small commits for more convenient review (optional)
• PR title captures the intent of the changes, and is fitting for release notes.
• Updated documentation
• Ensured that unit tests are added for all new behavior (See
  Ground Rules),
  and changes to existing code have good test coverage.

Pre merge checklist

• Added appropriate release note label
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[codecov-commenter]

Codecov Report

Merging #6195 (d378257) into main (14162a9) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #6195      +/-   ##
==========================================
+ Coverage   82.63%   82.65%   +0.01%     
==========================================
  Files         347      347              
  Lines       21244    21244              
  Branches      848      848              
==========================================
+ Hits        17556    17559       +3     
+ Misses       3390     3387       -3     
  Partials      298      298              

Files	Coverage Δ
src/ert/analysis/_es_update.py	88.59% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[dafeda]

Based on discussion with users that are disabling parameters for update and the fact that they use the same parameters to drive the models, I think this change is safe to make.