[8.15](backport #4647) Remove Enterprise license message

[mergify]

Description

We no longer mention specific licenses in the docs and instead link users to the subscriptions page.
The link to the subscriptions page was added previously, but we need to remove the mention of the Enterprise license in the prereqs.

Documentation sets edited in this PR

Check all that apply.

• Stateful (docs/en/observability/*)
• Serverless (docs/en/serverless/*)
• Integrations Developer Guide (docs/en/integrations/*)
• None of the above

Related issue

Closes #

Checklist

• Product/Engineering Review
• Writer Review

Follow-up tasks

Select one.

• This PR does not need to be ported to another doc set because:
  • The concepts in this PR only apply to one doc set (serverless or stateful)
  • The PR contains edits to both doc sets (serverless and stateful)

---

This is an automatic backport of pull request #4647 done by [Mergify](https://mergify.com).

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