fix(plugin-shiki): remove duplicated rehypePlugin module

[chenjiahan]

Summary

Remove the duplicated rehypePlugin module (which is never used).

• https://github.com/web-infra-dev/rspress/blob/789cc8493f5493788f88d6ab479f6ac2c1a40a43/packages/plugin-shiki/src/rehypePlugin.ts
• https://github.com/web-infra-dev/rspress/blob/789cc8493f5493788f88d6ab479f6ac2c1a40a43/packages/plugin-shiki/src/shiki/rehypePlugin.ts

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[netlify]

✅ Deploy Preview for rspress-v2 ready!

Name	Link
🔨 Latest commit	f3eb18c
🔍 Latest deploy log	https://app.netlify.com/sites/rspress-v2/deploys/67f4d44d7f86cf00081e9fe8
😎 Deploy Preview	https://deploy-preview-2045--rspress-v2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[netlify]

✅ Deploy Preview for aquamarine-blini-95325f ready!

Name	Link
🔨 Latest commit	f3eb18c
🔍 Latest deploy log	https://app.netlify.com/sites/aquamarine-blini-95325f/deploys/67f4d44d5c2de30008320dac
😎 Deploy Preview	https://deploy-preview-2045--aquamarine-blini-95325f.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
Lighthouse	1 paths audited Performance: 94 (🟢 up 15 from production) Accessibility: 97 (no change from production) Best Practices: 92 (🟢 up 9 from production) SEO: 100 (no change from production) PWA: - View the detailed breakdown and full score reports

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[chenjiahan]

Duplicated #2046