Remove support for x-gitbook-host in v2

[SamyPesse]

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[changeset-bot]

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Latest commit: 12bae27

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[github-actions]

Summary of the deployments:

Version 1 (production)

Version	URL	Status
Latest commit	https://8f835f41.gitbook-open.pages.dev	✅
PR	https://pr2918.gitbook-open.pages.dev	✅

Version 2 (experimental)

Version	URL	Status
Vercel	https://gitbook-v2-lse22a78b-gitbook.vercel.app	✅
Cloudflare		❌

Test content

Site	v1	v2
GitBook	https://8f835f41.gitbook-open.pages.dev/docs.gitbook.com	https://gitbook-v2-lse22a78b-gitbook.vercel.app/url/docs.gitbook.com
E2E	https://8f835f41.gitbook-open.pages.dev/gitbook.gitbook.io/test-gitbook-open	https://gitbook-v2-lse22a78b-gitbook.vercel.app/url/gitbook.gitbook.io/test-gitbook-open

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Build	Status	Details	Updated (UTC)
customers (Inspect)	👍 Changes approved	2 changed	Mar 4, 2025, 5:33 PM
customers-v2 (Inspect)	👍 Changes approved	11 changed	Mar 4, 2025, 5:35 PM
default (Inspect)	👍 Changes approved	8 changed	Mar 4, 2025, 5:35 PM