moved DELETE agent_config body to query params

[bryce-b]

Summary

Resolved #198019. It's unclear why exactly this error was occurring to begin with, I didn't have luck with refactoring the ts-io parameters using body so I opted to move them to the query list.
I wasn't sure if the query parameters needed to be listed individually, or if I could re-use the serviceRt type.

Additionally, does the date on the API need to be updated?
Does this count as a breaking change?

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Check the PR satisfies following conditions.

Reviewers should verify this PR satisfies this list as well.

• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for breaking HTTP API changes, and any breaking changes have been approved by the breaking-change committee. The release_note:breaking label should be applied in these situations.
• [ x ] The PR description includes the appropriate Release Notes section, and the correct release_node:* label is applied per the guidelines

[elasticmachine]

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