delete the transform to delete any docs which might have been written by the (#52360)

delete the transform to delete any docs which might have been written by the task after deleting
the index

fixes #51347

x-pack/plugin/transform/qa/single-node-tests/src/test/java/org/elasticsearch/xpack/transform/integration/TransformRobustnessIT.java

@@ -90,6 +90,9 @@ public class TransformRobustnessIT extends TransformRestTestCase {
 
         // the task is gone
         assertEquals(0, getNumberOfTransformTasks());
+
+        // delete the transform because the task might have written a state doc, cleanup fails if the index isn't empty
+        deleteTransform(transformId);
     }
 
     @SuppressWarnings("unchecked")