Remove unused private function

[mwcraig]

Please have a look at the following list and replace the "[ ]" with a "[x]" if
the answer to this question is yes.

• For new contributors: Did you add yourself to the "Authors.rst" file?

For documentation changes:

• For documentation changes: Does your commit message include a "[skip ci]"?
  Note that it should not if you changed any examples!

For bugfixes:

• Did you add an entry to the "Changes.rst" file?
• Did you add a regression test?
• Does the commit message include a "Fixes #issue_number" (replace "issue_number").
• Does this PR add, rename, move or remove any existing functions or parameters?

Please note that the last point is not a requirement. It is meant as a check if
the pull request potentially breaks backwards-compatibility.

---

Fixes #868

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.95%. Comparing base (b7a32bb) to head (de46dd4).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #869      +/-   ##
==========================================
- Coverage   97.96%   97.95%   -0.02%     
==========================================
  Files           9        9              
  Lines        1379     1369      -10     
==========================================
- Hits         1351     1341      -10     
  Misses         28       28              

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