RunKit is referenced in the docs, but the service is dead

[alxndrsn]

• Extension Name: directive, hook-data, code-format, code-preview, alert, hook-frontmatter, sequential-hooks, footnote, shiki
• Extension Version:

Documentation Is:

• Missing
• Needed
• Confusing
• Not Sure?

Docs reference RunKit, but the service is dead (https://github.com/orgs/community/discussions/141424). Their servers either 503, or serve an expired HTTPS cert and then 503.

Your proposal for changes

Remove references to:

• https://badge.runkitcdn.com/example.html.svg
• https://untitled-0x6rqd9q0jep.runkit.sh/
• https://untitled-fmwk1u13dn8y.runkit.sh/
• etc.