remove misleading comment

Descriptions of the changes in this PR:

*Motivation*

ParallelRead is actually used internally at ledger recovery. It is used at production.

*Changes*

Removed misleading comment.




Reviewers: Enrico Olivelli <eolivelli@gmail.com>, Jia Zhai <None>

This closes apache#1671 from sijie/remove_misleading_comment

bookkeeper-server/src/main/java/org/apache/bookkeeper/client/PendingReadOp.java

@@ -487,7 +487,6 @@ public ScheduledFuture<?> getSpeculativeTask() {
         return speculativeTask;
     }
 
-    // I don't think this is ever used in production code -Ivan
     PendingReadOp parallelRead(boolean enabled) {
         this.parallelRead = enabled;
         return this;