docs: Remove references to unversioned CDN links

[rolodato]

Thanks for submitting a PR! Please check the boxes below:

• I have added information to docs/ if required so people know about the feature!
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• I have filled in the "How did you test this code" section below?
• I have used a Conventional Commit title for this Pull Request

Changes

This change removes unversioned CDN links as a suggested installation method to get started using the client-side JS SDK.

After #4767 was released, we now have proper versioned CDN links in our docs if customers really need it.

How did you test this code?

Running frontend locally:

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
flagsmith-frontend-preview	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Nov 1, 2024 0:34am
flagsmith-frontend-staging	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Nov 1, 2024 0:34am

1 Skipped Deployment

Name	Status	Preview	Comments	Updated (UTC)
docs	⬜️ Ignored (Inspect)			Nov 1, 2024 0:34am

[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-api-test:pr-4792	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-e2e:pr-4792	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api:pr-4792	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-4792	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-4792	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-frontend:pr-4792	Finished ✅	Results ✅

[github-actions]

Uffizzi Ephemeral Environment deployment-57838

☁️ https://app.uffizzi.com/github.com/Flagsmith/flagsmith/pull/4792

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