chore: clean up admonitions

[vinckr]

• chore: outdated notice

• chore: clean up admonitions

• removes some outdated admonitions

• removes admonitions in documents where there are already a lot (to reduce overload of admonitions)

• fixes some minor spelling and formatting issues

• updates some boxy links that we missed

Related Issue or Design Document

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
  If this pull request addresses a security vulnerability,
  I confirm that I got approval (please contact [email protected]) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added the necessary documentation within the code base (if appropriate).

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