Remove the last readFrom from xpack

This the last Writeable#readFrom in xpack!

Original commit: elastic/x-pack-elasticsearch@5412160bdd

elasticsearch/x-pack/marvel/src/main/java/org/elasticsearch/marvel/action/MonitoringBulkResponse.java

@@ -87,6 +87,11 @@ public class MonitoringBulkResponse extends ActionResponse {
             this(in.<Throwable>readThrowable());
         }
 
+        @Override
+        public void writeTo(StreamOutput out) throws IOException {
+            out.writeThrowable(getCause());
+        }
+
         /**
          * The failure message.
          */
@@ -108,16 +113,6 @@ public class MonitoringBulkResponse extends ActionResponse {
             return cause;
         }
 
-        @Override
-        public Error readFrom(StreamInput in) throws IOException {
-            return new Error(in);
-        }
-
-        @Override
-        public void writeTo(StreamOutput out) throws IOException {
-            out.writeThrowable(getCause());
-        }
-
         @Override
         public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
             builder.startObject();