[8.6] [DOCS] Remove OAS API previews (elastic#168761) (elastic#169145)

# Backport

This will backport the following commits from `main` to `8.6`:
- [[DOCS] Remove OAS API previews
(elastic#168761)](elastic#168761)

<!--- Backport version: 8.9.8 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

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Remove OAS API previews
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Remove OAS API previews
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Remove OAS API previews
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BACKPORT-->