Small refactor to HERDManager

[mavaylon1]

Clean up HERDManager due to some updated logic downstream in pynwb
What was the reasoning behind this change? Please explain the changes briefly.

How to test the behavior?

Show how to reproduce the new behavior (can be a bug fix or a new feature)

Checklist

• Did you update CHANGELOG.md with your changes?
• Does the PR clearly describe the problem and the solution?
• Have you reviewed our Contributing Guide?
• Does the PR use "Fix #XXX" notation to tell GitHub to close the relevant issue numbered XXX when the PR is merged?

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.62%. Comparing base (81760b8) to head (7024a24).
⚠️ Report is 30 commits behind head on dev.

Files with missing lines	Patch %	Lines
src/hdmf/container.py	84.61%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1292      +/-   ##
==========================================
- Coverage   91.63%   91.62%   -0.02%     
==========================================
  Files          42       42              
  Lines        9672     9684      +12     
  Branches     1962     1963       +1     
==========================================
+ Hits         8863     8873      +10     
- Misses        522      523       +1     
- Partials      287      288       +1     

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[mavaylon1]

Review Notes: This is for pynwb ticket NeurodataWithoutBorders/pynwb#2111