fix(integrations): remove wandb.sklearn.plot_decision_boundaries that contains dead logic

[kptkin]

Fixes WB-8772

Description

What does the PR do?

This PR remove the wandb.sklearn.plot_decision_boundaries as this function depends on a DBPlot class from a third party library that we used to port (https://github.com/tmadl/highdimensional-decision-boundary-plot) and the relevant class gist can be seen here: https://gist.github.com/morganmcg1/d40cdf9ec0f4a88a8bf028b63e768978

This change won't affect any user since we didn't have any users actively using this feature (the issue was found internally) and we still leave the actual visualization logic, if users compute their own decision boundaries it seems reasonable to avoid maintenance of this third party code.

Testing

How was this PR tested?

Checklist

• Include reference to internal ticket "Fixes WB-NNNN" and/or GitHub issue "Fixes #NNNN" (if applicable)
• Ensure PR title compliance with the conventional commits standards

[codecov]

Codecov Report

Merging #4348 (1fe24c9) into main (eddc2ac) will decrease coverage by 0.21%.
The diff coverage is n/a.

❗ Current head 1fe24c9 differs from pull request most recent head 8bfd127. Consider uploading reports for the commit 8bfd127 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4348      +/-   ##
==========================================
- Coverage   83.03%   82.81%   -0.22%     
==========================================
  Files         258      248      -10     
  Lines       32870    32176     -694     
==========================================
- Hits        27292    26646     -646     
+ Misses       5578     5530      -48     

Flag	Coverage Δ
functest	56.63% <ø> (-0.23%)	⬇️
unittest	72.69% <ø> (-0.48%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
wandb/sklearn/__init__.py	100.00% <ø> (ø)
wandb/sklearn/plot/__init__.py	100.00% <ø> (ø)
wandb/sklearn/plot/classifier.py	97.05% <ø> (+8.90%)	⬆️
wandb/sdk/internal/settings_static.py	91.30% <0.00%> (-2.45%)	⬇️
wandb/sdk/internal/internal_api.py	87.64% <0.00%> (-1.28%)	⬇️
wandb/sdk/interface/interface_shared.py	86.56% <0.00%> (-0.78%)	⬇️
wandb/sdk/wandb_artifacts.py	83.19% <0.00%> (-0.63%)	⬇️
wandb/sdk/lib/git.py	79.01% <0.00%> (-0.62%)	⬇️
wandb/sync/sync.py	89.59% <0.00%> (-0.38%)	⬇️
wandb/sdk/verify/verify.py	33.33% <0.00%> (-0.37%)	⬇️
... and 36 more