docs: remove useless comment

[slorber]

Motivation

Useless doc comment, only in beta.13 version, triggers a warning:

[WARNING] Docs markdown link couldn't be resolved: (./api/lifecycle-apis.md) in /Users/sebastienlorber/Desktop/projects/docusaurus/website/versioned_docs/version-2.0.0-beta.13/using-themes.md for version 2.0.0-beta.13

[netlify]

✔️ [V2]

🔨 Explore the source changes: 1ae1e46

🔍 Inspect the deploy log: https://app.netlify.com/sites/docusaurus-2/deploys/61c30e7ca077df000804cf2a

😎 Browse the preview: https://deploy-preview-6159--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	64
🟢 Accessibility	98
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-6159--docusaurus-2.netlify.app/

[github-actions]

Size Change: 0 B

Total Size: 662 kB

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	40.1 kB
website/build/assets/css/styles.********.css	102 kB
website/build/assets/js/main.********.js	490 kB
website/build/index.html	29.6 kB

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