Remove unused field (elastic#127494)

Author: Yuristry

server/src/main/java/org/elasticsearch/indices/IndexingMemoryController.java

@@ -248,15 +248,15 @@ protected void deactivateThrottling(IndexShard shard) {
 
     @Override
     public void postIndex(ShardId shardId, Engine.Index index, Engine.IndexResult result) {
-        postOperation(shardId, index, result);
+        postOperation(index, result);
     }
 
     @Override
     public void postDelete(ShardId shardId, Engine.Delete delete, Engine.DeleteResult result) {
-        postOperation(shardId, delete, result);
+        postOperation(delete, result);
     }
 
-    private void postOperation(ShardId shardId, Engine.Operation operation, Engine.Result result) {
+    private void postOperation(Engine.Operation operation, Engine.Result result) {
         recordOperationBytes(operation, result);
         // Piggy back on indexing threads to write segments. We're not submitting a task to the index threadpool because we want memory to
         // be reclaimed rapidly. This has the downside of increasing the latency of _bulk requests though. Lucene does the same thing in