remove unused functions

modules/tree/src/main/tree.scala

@@ -290,10 +290,4 @@ object Node {
       node.mainlineNodeList.map(minimalNodeJsonWriter.writes)
     }
   }
-
-  private def add[A](k: String, v: A, cond: Boolean)(o: JsObject)(implicit writes: Writes[A]): JsObject =
-    if (cond) o + (k -> writes.writes(v)) else o
-
-  private def add[A: Writes](k: String, v: Option[A]): JsObject => JsObject =
-    v.fold(identity[JsObject] _) { add(k, _, true) _ }
 }