[SPARK-15087][MINOR][DOC] Follow Up: Fix the Comments

## What changes were proposed in this pull request?
Remove the Comment, since it not longer applies. see the discussion here(https://github.com/apache/spark/pull/12865#discussion-diff-61946906)

Author: Sandeep Singh <sandeep@techaddict.me>

Closes #12953 from techaddict/SPARK-15087-FOLLOW-UP.

core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala

@@ -389,11 +389,6 @@ private[spark] class TaskSchedulerImpl(
     // (taskId, stageId, stageAttemptId, accumUpdates)
     val accumUpdatesWithTaskIds: Array[(Long, Int, Int, Seq[AccumulableInfo])] = synchronized {
       accumUpdates.flatMap { case (id, updates) =>
-        // We should call `acc.value` here as we are at driver side now.  However, the RPC framework
-        // optimizes local message delivery so that messages do not need to de serialized and
-        // deserialized.  This brings trouble to the accumulator framework, which depends on
-        // serialization to set the `atDriverSide` flag.  Here we call `acc.localValue` instead to
-        // be more robust about this issue.
         val accInfos = updates.map(acc => acc.toInfo(Some(acc.value), None))
         taskIdToTaskSetManager.get(id).map { taskSetMgr =>
           (id, taskSetMgr.stageId, taskSetMgr.taskSet.stageAttemptId, accInfos)