add deprecation warnings to unused functions

[CloseChoice]

Overview

Works towards #3507

Description of the changes proposed in this pull request:

• add deprecation warning for unused code

Checklist

• All pre-commit checks pass.
• [ ] Unit tests added (if fixing a bug or adding a new feature)

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (584fb9c) 59.38% compared to head (7de0c4b) 59.37%.

Files	Patch %	Lines
shap/explainers/_explainer.py	50.00%	1 Missing ⚠️
shap/plots/_text.py	50.00%	1 Missing ⚠️
shap/utils/_masked_model.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3516      +/-   ##
==========================================
- Coverage   59.38%   59.37%   -0.01%     
==========================================
  Files          90       90              
  Lines       12733    12739       +6     
==========================================
+ Hits         7561     7564       +3     
- Misses       5172     5175       +3     

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[connortann]

LGTM. I think before fully removing text_old for example I'd want to fully read through both functions to understand the differences and ensure nothing of value is lost; but in any case raising the warning seems like a good place to start.