Remove childrenStats.

Author: concretevitamin

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala

@@ -40,10 +40,11 @@ abstract class LogicalPlan extends QueryPlan[LogicalPlan] {
    *                    defaults to the product of children's `sizeInBytes`.
    */
   case class Statistics(
-    sizeInBytes: Long = childrenStats.map(_.sizeInBytes).product
+    sizeInBytes: Long
+  )
+  lazy val statistics: Statistics = Statistics(
+    sizeInBytes = children.map(_.statistics).map(_.sizeInBytes).product
   )
-  lazy val statistics: Statistics = new Statistics
-  lazy val childrenStats = children.map(_.statistics)
 
   /**
    * Returns the set of attributes that are referenced by this node