Revert "Support flattened data_stream.* fields under Elastic-Agent"

[belimawr]

Reverts #36516 because it broke inputs when running under Elastic-Agent

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @belimawr? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[elasticmachine]

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• Start Time: 2023-09-18T17:55:21.819+0000

• Duration: 68 min 32 sec

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Test	Results
Failed	0
Passed	8311
Skipped	379
Total	8690

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