Remove HTML4 Forcing in Online Docs

[mrmundt]

Fixes NA

Summary/Motivation:

We have been forcing HTML4 ReadTheDocs configuration due to an issue from 2021; however, that issue has been resolved.

Changes proposed in this PR:

• Allow RTD to render HTML in whatever format it likes

Legal Acknowledgement

By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

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]

I don't like removing breadcrumbs in case this pops up again, but I know you have an aversion to leaving historical comments.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (1cb37aa) 87.82% compared to head (fefbd4c) 87.82%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2949   +/-   ##
=======================================
  Coverage   87.82%   87.82%           
=======================================
  Files         770      770           
  Lines       89654    89654           
=======================================
  Hits        78741    78741           
  Misses      10913    10913           

Flag	Coverage Δ
linux	84.86% <ø> (ø)
osx	74.58% <ø> (ø)
other	85.04% <ø> (ø)
win	82.11% <ø> (ø)

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