Update ko/_toctree.yml and remove custom_tools.md to reflect latest changes

[jungnerd]

What does this PR do?

Update ko/_toctree.yml and remove custom_tools.md to reflect latest changes.
Thank you in advance for your review.

Part of #20179

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

May you review this PR?
@stevhliu

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[stevhliu]

Thanks for updating with the toctree with the new quantization methods!