Persistent Tasks: remove unused isCurrentStatus method (#2076)

Removes a method that is no longer used in production code.

Relates to #957

server/src/main/java/org/elasticsearch/persistent/PersistentTasksCustomMetaData.java

@@ -406,14 +406,6 @@ public final class PersistentTasksCustomMetaData extends AbstractNamedDiffable<M
             return status;
         }
 
-        /**
-         * @return Whether the task status isn't stale. When a task gets unassigned from the executor node or assigned
-         * to a new executor node and the status hasn't been updated then the task status is stale.
-         */
-        public boolean isCurrentStatus() {
-            return allocationIdOnLastStatusUpdate != null && allocationIdOnLastStatusUpdate == allocationId;
-        }
-
         @Override
         public XContentBuilder toXContent(XContentBuilder builder, ToXContent.Params xParams) throws IOException {
             builder.startObject();

server/src/test/java/org/elasticsearch/persistent/PersistentTasksExecutorIT.java

@@ -202,7 +202,7 @@ public class PersistentTasksExecutorIT extends ESIntegTestCase {
             int finalI = i;
             WaitForPersistentTaskStatusFuture<?> future1 = new WaitForPersistentTaskStatusFuture<>();
             persistentTasksService.waitForPersistentTaskStatus(taskId,
-                    task -> task != null && task.isCurrentStatus() && task.getStatus().toString() != null &&
+                    task -> task != null && task.getStatus() != null && task.getStatus().toString() != null &&
                             task.getStatus().toString().equals("{\"phase\":\"phase " + (finalI + 1) + "\"}"),
                     TimeValue.timeValueSeconds(10), future1);
             assertThat(future1.get().getId(), equalTo(taskId));