CLN: Old helper functions

[mroeschke]

• closes CLN/DEPR: Undocumented, old helper functions #21838
• passes git diff upstream/master -u -- "*.py" | flake8 --diff

It appears that these functions were helpers at one point in the past, but they don't appear anywhere in the codebase now (and are not publicly documented).

I think they are safe to blow away, although they exist the public namespace.

[jbrockmendel]

Tests.io.test_sql needs format

[jbrockmendel]

Although the name makes grepping for it pretty much impossible

[codecov]

Codecov Report

Merging #22104 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #22104      +/-   ##
==========================================
+ Coverage   92.06%   92.06%   +<.01%     
==========================================
  Files         170      170              
  Lines       50705    50691      -14     
==========================================
- Hits        46680    46669      -11     
+ Misses       4025     4022       -3

Flag	Coverage Δ
#multiple	90.47% <100%> (ø)	⬆️
#single	42.31% <100%> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/core/reshape/util.py	100% <ø> (+9.67%)	⬆️
pandas/core/tools/datetimes.py	84.78% <100%> (-0.44%)	⬇️

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[jreback]

thanks @mroeschke