Simplify Custom PyROS Domain Validators

[shermanjasonaf]

Summary/Motivation:

Following #3159 and this comment in #3126, this PR simplifies a few custom PyROS domain validators which do not require statefulness.

Changes proposed in this PR:

Simplify custom PyROS domain validators.

Legal Acknowledgement

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1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[jsiirola]

One super-minor change (that was not technically part of this PR, but should be fixed).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.37%. Comparing base (26e4970) to head (3797608).
Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3169      +/-   ##
==========================================
- Coverage   88.38%   88.37%   -0.01%     
==========================================
  Files         846      846              
  Lines       94857    94853       -4     
==========================================
- Hits        83835    83831       -4     
  Misses      11022    11022              

Flag	Coverage Δ
linux	86.33% <100.00%> (-0.01%)	⬇️
osx	75.72% <100.00%> (-0.01%)	⬇️
other	86.52% <100.00%> (-0.01%)	⬇️
win	83.81% <100.00%> (-0.01%)	⬇️

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