Cleaning up the docs

[john-science]

What is the change? Why is it being made?

Cleaning up the docs by:

1. Removing empty "Applications" section from the docs Gallery
2. Removing unwanted file paths from pytest verbose output table.
3. Trying to fix wonky headers in gallery section.

SCR Information

Change Type: docs

One-Sentence Rationale: We want to make sure the docs render well in PDF.

One-line Impact on Requirements: NA

---

Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify any new/changed code.
• The documentation is still up-to-date in the doc folder.
• The code style follows good practices.
• The dependencies are still up-to-date in pyproject.toml.

[john-science]

Okay! It looks like it works to me. Take a look: https://github.com/terrapower/armi/actions/runs/20355694658?pr=2395

[opotowsky]

Yay for stackoverflow! Outlines look great