Removes tech preview banners and technical preview limitations page

[benironside]

Important

Do not merge until Nov 20.

Resolves https://github.com/elastic/security-docs-internal/issues/41 by removing the "Technical Preview" badges at the top of every serverless docs page. Also removes the Technical preview limitations page entirely.

Previews

There's too many affected pages to check them all, but some spot-checking would be good.

[github-actions]

A documentation preview will be available soon.

• 🔨 Buildkite builds
• 📚 HTML diff
• 📙 Preview page

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• Rebuild this PR and all Elastic docs: run docs-build rebuild

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[mergify]

This pull request does not have a backport label. Could you fix it @benironside? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• v7.x is the label to automatically backport to the 7.x branch.
• v7./d./d is the label to automatically backport to the 7./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[nastasha-solomon]

I did the following to review this PR and found no major issues:

• Spot-checked the output to see if there were any formatting issues that came from removing the tech preview tag. I didn't notice any.

• Pulled down the branch to check for remaining instances of the preview:[] tag. There are only a handful, and each instance looks to be necessary and correct.