[SPARK-23243][CORE][FOLLOWUP] Remove todo added by SPARK-23207

### What changes were proposed in this pull request?
PR #22112 fixed the todo added by PR #20393(SPARK-23207). We can remove it now.

### Why are the changes needed?
In order not to confuse developers.

### Does this PR introduce any user-facing change?
no

### How was this patch tested?
no need to test

Closes #25755 from LinhongLiu/remove-todo.

Authored-by: Liu,Linhong <liulinhong@baidu.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

core/src/main/scala/org/apache/spark/rdd/RDD.scala

@@ -430,8 +430,6 @@ abstract class RDD[T: ClassTag](
    *
    * If you are decreasing the number of partitions in this RDD, consider using `coalesce`,
    * which can avoid performing a shuffle.
-   *
-   * TODO Fix the Shuffle+Repartition data loss issue described in SPARK-23207.
    */
   def repartition(numPartitions: Int)(implicit ord: Ordering[T] = null): RDD[T] = withScope {
     coalesce(numPartitions, shuffle = true)