Fix/code maintenance after dependencies update

[madtoinou]

Checklist before merging this PR:

• Mentioned all issues that this PR fixes or addresses.
• Summarized the updates of this PR under Summary.
• Added an entry under Unreleased in the Changelog.

Summary

• replace the deprecated _validate_data call with validate_data
• removed unnecessary logic around sklearn version
• removed unnecessary logic around statsmodel version

Other Information

Could not solve a lot of the deprecation warnings as they were occurring in the dependencies (prophet, shap, lightgbm, ...) so this PR is smaller than I would have liked...

[dennisbader]

Looks great, thanks a lot @madtoinou 🚀

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.25%. Comparing base (f1850d6) to head (5f01eea).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2722      +/-   ##
==========================================
- Coverage   94.29%   94.25%   -0.05%     
==========================================
  Files         142      142              
  Lines       15647    15635      -12     
==========================================
- Hits        14755    14736      -19     
- Misses        892      899       +7     

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