docs: remove unreachable rich tweets link

[ya-nsh]

Summary

• remove the unreachable rich-tweets external link from the main README and translated READMEs
• remove the same dead URL from the benchmark markdown snippet so the repository no longer references it

Validation

• curl -I -L --max-time 15 https://www.willmcgugan.com/blog/pages/post/rich-tweets/ timed out
• curl -I -L --max-time 15 https://willmcgugan.com/blog/pages/post/rich-tweets/ timed out
• rg 'rich-tweets|willmcgugan.com/blog/pages/post/rich-tweets' -n . returns no matches
• python -m py_compile benchmarks/snippets.py
• git diff --check

Closes #4123

[ya-nsh]

Friendly review ping: this PR is ready for maintainer review when you get a chance. No required checks are showing on the PR from my side.

Happy to adjust quickly if you want a different shape or narrower scope.