rm old comment on HHWheelTimer::UniquePtr

Summary: This comment is outdated.

Reviewed By: yfeldblum

Differential Revision: D5730049

fbshipit-source-id: f6088c4354210fafb019656cdf8246abf90fbc06

folly/io/async/HHWheelTimer.h

@@ -54,7 +54,6 @@ namespace folly {
 class HHWheelTimer : private folly::AsyncTimeout,
                      public folly::DelayedDestruction {
  public:
-  // This type has always been a misnomer, because it is not a unique pointer.
   using UniquePtr = std::unique_ptr<HHWheelTimer, Destructor>;
   using SharedPtr = std::shared_ptr<HHWheelTimer>;