do not include the index in toString (#5268)

server/src/main/java/io/druid/segment/realtime/FireHydrant.java

@@ -141,8 +141,9 @@ public class FireHydrant
   @Override
   public String toString()
   {
+    // Do not include IncrementalIndex in toString as AbstractIndex.toString() actually prints
+    // all the rows in the index
     return "FireHydrant{" +
-           "index=" + index +
            ", queryable=" + adapter.get().getIdentifier() +
            ", count=" + count +
            '}';