Remove @UpdateForV9 annotation from ReindexRequest#failOnSizeSpecified

We do need this check to make sure we don't silently accept requests
with ignored `size` parameter specified since `max_docs` is optional.
We want to notify users that they must use `max_docs` and specifying `size`
is a mistake.

This behaviour is tested in the `reindex/20_validation/specifying size fails` test.

Author: arteam

server/src/main/java/org/elasticsearch/index/reindex/ReindexRequest.java

@@ -21,7 +21,6 @@
 import org.elasticsearch.common.settings.SecureString;
 import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.core.TimeValue;
-import org.elasticsearch.core.UpdateForV9;
 import org.elasticsearch.features.NodeFeature;
 import org.elasticsearch.index.VersionType;
 import org.elasticsearch.index.query.QueryBuilder;
@@ -499,8 +498,6 @@ static void setMaxDocsValidateIdentical(AbstractBulkByScrollRequest<?> request,
         }
     }
 
-    @UpdateForV9(owner = UpdateForV9.Owner.DISTRIBUTED_INDEXING)
-    // do we still need this ref to [max_docs] or can we remove the field entirely so it's rejected with the default message?
     private static void failOnSizeSpecified() {
         throw new IllegalArgumentException("invalid parameter [size], use [max_docs] instead");
     }