Remove unused hook_manager_run_workflow

[eivindjahren]

Pre review checklist

• Added appropriate release note label
• PR title captures the intent of the changes, and is fitting for release notes.
• Commit history is consistent and clean, in line with the contribution guidelines.

Adding labels helps the maintainers when writing release notes. This is the list of release note labels.

[codecov-commenter]

Codecov Report

Merging #4008 (f10f0c8) into main (f3e3a89) will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #4008      +/-   ##
==========================================
+ Coverage   58.43%   58.49%   +0.05%     
==========================================
  Files         542      542              
  Lines       40483    40473      -10     
  Branches     3685     3683       -2     
==========================================
+ Hits        23656    23673      +17     
+ Misses      15811    15784      -27     
  Partials     1016     1016              

Impacted Files	Coverage Δ
src/clib/lib/enkf/hook_manager.cpp	0.00% <ø> (ø)
src/ert/job_runner/job.py	72.78% <0.00%> (+2.04%)	⬆️
src/ert/gui/ertwidgets/validationsupport.py	98.63% <0.00%> (+19.17%)	⬆️

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