[8.x] CsvTestsDataLoader::deleteInferenceEndpoint should use Delete Inference API with task-type (#115832)

This commit updates CsvTestsDataLoader::deleteInferenceEndpoint to use the form of the Delete Inference API that accepts a task type.

The test infrastructure attempts to delete the inference endpoint with a request of the form DELETE /_inference/<inference_id>. This form was introduced in 8.13 (see #104483). Previously, the task type was the only supported form, e.g.  DELETE /_inference/<task_type>/<inference_id>.

Since the task-type form is supported on both recent and less recent Elasticsearch versions, then it's probably most straightforward to just use that form in the 8.x branch.

Additional, this commit unmutes the org.elasticsearch.xpack.esql.qa.mixed.MixedClusterEsqlSpecIT test suite, since this fix allows the suite to complete successfully.

closes #115315

Author: ChrisHegarty

muted-tests.yml

@@ -321,8 +321,6 @@ tests:
 - class: org.elasticsearch.xpack.inference.TextEmbeddingCrudIT
   method: testPutE5Small_withPlatformSpecificVariant
   issue: https://github.com/elastic/elasticsearch/issues/113950
-- class: org.elasticsearch.xpack.esql.qa.mixed.MixedClusterEsqlSpecIT
-  issue: https://github.com/elastic/elasticsearch/issues/115315
 - class: org.elasticsearch.upgrades.UpgradeClusterClientYamlTestSuiteIT
   method: test {p0=mixed_cluster/80_transform_jobs_crud/Test GET, start, and stop old cluster batch transforms}
   issue: https://github.com/elastic/elasticsearch/issues/115319

x-pack/plugin/esql/qa/testFixtures/src/main/java/org/elasticsearch/xpack/esql/CsvTestsDataLoader.java

@@ -272,7 +272,7 @@ public static void createInferenceEndpoint(RestClient client) throws IOException
 
     public static void deleteInferenceEndpoint(RestClient client) throws IOException {
         try {
-            client.performRequest(new Request("DELETE", "_inference/test_sparse_inference"));
+            client.performRequest(new Request("DELETE", "_inference/sparse_embedding/test_sparse_inference"));
         } catch (ResponseException e) {
             // 404 here means the endpoint was not created
             if (e.getResponse().getStatusLine().getStatusCode() != 404) {