[TEST] Fix backport of #30941 (#30954)

The implementation of #30941 used functionality that is only
available in 6.4 and higher.  This changes the implementation in
6.3 to one that is less elegant but still uses ML endpoints
rather than retrieving the cluster state directly.

Author: droberts195

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ml/integration/MlRestTestStateCleaner.java

@@ -6,8 +6,6 @@
 package org.elasticsearch.xpack.core.ml.integration;
 
 import org.apache.logging.log4j.Logger;
-import org.elasticsearch.client.Request;
-import org.elasticsearch.client.Response;
 import org.elasticsearch.client.RestClient;
 import org.elasticsearch.common.xcontent.support.XContentMapValues;
 import org.elasticsearch.test.rest.ESRestTestCase;
@@ -37,12 +35,9 @@ public void clearMlMetadata() throws IOException {
 
     @SuppressWarnings("unchecked")
     private void deleteAllDatafeeds() throws IOException {
-        final Request datafeedsRequest = new Request("GET", "/_xpack/ml/datafeeds");
-        datafeedsRequest.addParameter("filter_path", "datafeeds");
-        final Response datafeedsResponse = adminClient.performRequest(datafeedsRequest);
-        @SuppressWarnings("unchecked")
+        final Map<String, Object> datafeedsAsMap = testCase.entityAsMap(adminClient.performRequest("GET", "/_xpack/ml/datafeeds"));
         final List<Map<String, Object>> datafeeds =
-                (List<Map<String, Object>>) XContentMapValues.extractValue("datafeeds", testCase.entityAsMap(datafeedsResponse));
+                (List<Map<String, Object>>) XContentMapValues.extractValue("datafeeds", datafeedsAsMap);
         if (datafeeds == null) {
             return;
         }
@@ -79,12 +74,10 @@ private void deleteAllDatafeeds() throws IOException {
     }
 
     private void deleteAllJobs() throws IOException {
-        final Request jobsRequest = new Request("GET", "/_xpack/ml/anomaly_detectors");
-        jobsRequest.addParameter("filter_path", "jobs");
-        final Response response = adminClient.performRequest(jobsRequest);
+        final Map<String, Object> jobsAsMap = testCase.entityAsMap(adminClient.performRequest("GET", "/_xpack/ml/anomaly_detectors"));
         @SuppressWarnings("unchecked")
         final List<Map<String, Object>> jobConfigs =
-                (List<Map<String, Object>>) XContentMapValues.extractValue("jobs", testCase.entityAsMap(response));
+                (List<Map<String, Object>>) XContentMapValues.extractValue("jobs", jobsAsMap);
         if (jobConfigs == null) {
             return;
         }