fix: revert changes to MlEvaluateDataFrameResponse from #5622 (#5648)

* removes duplicated `ResponseBody`
* moves body back to `Response`
* removes `@variants: container` from Response

Author: MattDevy

output/openapi/elasticsearch-openapi.json

@@ -1,7 +1,6 @@
 {
   "endpointErrors": {},
   "generalErrors": [
-    "ResponseBody is present in multiple namespaces: _global.search and ml.evaluate_data_frame",
     "Dangling type '_global.scripts_painless_execute:PainlessExecutionPosition'",
     "Dangling type '_global.scripts_painless_execute:PainlessScript'",
     "Dangling type '_global.search._types:HitMetadata'",

output/openapi/elasticsearch-serverless-openapi.json

@@ -24,24 +24,20 @@ import {
 } from './types'
 
 export class Response {
-  /** @codegen_name result */
-  body: ResponseBody
-}
-
-/** @variants container */
-export class ResponseBody {
-  /**
-   * Evaluation results for a classification analysis.
-   * It outputs a prediction that identifies to which of the classes each document belongs.
-   */
-  classification?: DataframeClassificationSummary
-  /**
-   * Evaluation results for an outlier detection analysis.
-   * It outputs the probability that each document is an outlier.
-   */
-  outlier_detection?: DataframeOutlierDetectionSummary
-  /**
-   * Evaluation results for a regression analysis which outputs a prediction of values.
-   */
-  regression?: DataframeRegressionSummary
+  body: {
+    /**
+     * Evaluation results for a classification analysis.
+     * It outputs a prediction that identifies to which of the classes each document belongs.
+     */
+    classification?: DataframeClassificationSummary
+    /**
+     * Evaluation results for an outlier detection analysis.
+     * It outputs the probability that each document is an outlier.
+     */
+    outlier_detection?: DataframeOutlierDetectionSummary
+    /**
+     * Evaluation results for a regression analysis which outputs a prediction of values.
+     */
+    regression?: DataframeRegressionSummary
+  }
 }