Don't preserve indices between enrich qa tests.

This was added because it was suspected to cause the monitoring
enrich verification to fail, but that is not the case.

See #48258

x-pack/plugin/enrich/qa/common/src/main/java/org/elasticsearch/test/enrich/CommonEnrichRestTestCase.java

@@ -50,12 +50,6 @@ public void deletePolicies() throws Exception {
         }
     }
 
-    @Override
-    protected boolean preserveIndicesUponCompletion() {
-        // In order to avoid monitoring from failing exporting docs to monitor index.
-        return true;
-    }
-
     private void setupGenericLifecycleTest(boolean deletePipeilne) throws Exception {
         // Create source index:
         createSourceIndex("my-source-index");