add another delete-by-query deprecation

src/main/java/org/elasticsearch/index/engine/DeleteByQueryFailedEngineException.java

@@ -21,6 +21,8 @@ package org.elasticsearch.index.engine;
 
 import org.elasticsearch.index.shard.ShardId;
 
+/** @deprecated Delete-by-query is removed in 2.0, but we keep this so translog can replay on upgrade. */
+@Deprecated
 public class DeleteByQueryFailedEngineException extends EngineException {
 
     public DeleteByQueryFailedEngineException(ShardId shardId, Engine.DeleteByQuery deleteByQuery, Throwable cause) {