Java api: remove operationThreaded setter from ExplainRequestBuilder,…

… already available in base class SingleShardOperationRequestBuilder

It also didn't follow the setter convention that we adopted for request builders.
Fixed also javadocs warning caused byt missing descriptions for tag.

Closes #7186

src/main/java/org/elasticsearch/action/explain/ExplainRequestBuilder.java

@@ -110,10 +110,6 @@ public ExplainRequestBuilder setFields(String... fields) {
 
     /**
      * Indicates whether the response should contain the stored _source
-     *
-     *
-     * @param fetch
-     * @return
      */
     public ExplainRequestBuilder setFetchSource(boolean fetch) {
         FetchSourceContext context = request.fetchSourceContext();
@@ -167,14 +163,6 @@ public ExplainRequestBuilder setSource(BytesReference source, boolean unsafe) {
         return this;
     }
 
-    /**
-     * Sets whether the actual explain action should occur in a different thread if executed locally.
-     */
-    public ExplainRequestBuilder operationThreaded(boolean threadedOperation) {
-        request().operationThreaded(threadedOperation);
-        return this;
-    }
-
     protected void doExecute(ActionListener<ExplainResponse> listener) {
         if (sourceBuilder != null) {
             request.source(sourceBuilder);