Update a couple of comments

Summary:
The default timekeeper (`HeapTimekeeper`) has now microsecond resolution, so we don't need to advertise `ThreadWheelTimekeeperHighRes` (which I plan to deprecate) anymore.

Also fix a typo in the `HeapTimekeeper` description.

Reviewed By: luciang

Differential Revision: D49293397

fbshipit-source-id: 0e1282158987635613d747a42d9396571084c162

folly/experimental/coro/Sleep.h

@@ -27,17 +27,14 @@ namespace coro {
 
 /// Return a task that, when awaited, will sleep for the specified duration.
 ///
-/// Throws folly::OperationCancelled if cancellation is requested
-/// on the awaiting coroutine's associated CancellationToken.
-///
-/// NOTE: The default tk has Duration resolution, supply
-/// ThreadWheelTimekeeperHighRes for maximum sleep resolution
+/// Throws folly::OperationCancelled if cancellation is requested on the
+/// awaiting coroutine's associated CancellationToken.
 Task<void> sleep(HighResDuration d, Timekeeper* tk = nullptr);
 
 /// Return a task that, when awaited, will sleep for the specified duration.
 ///
-/// May complete sooner that the specified duration  if cancellation is
-/// requested on the awaiting coroutine's associated CancellationToken.
+/// May complete sooner that the specified duration if cancellation is requested
+/// on the awaiting coroutine's associated CancellationToken.
 Task<void> sleepReturnEarlyOnCancel(
     HighResDuration d, Timekeeper* tk = nullptr);
 

folly/futures/HeapTimekeeper.h

@@ -30,7 +30,7 @@
 namespace folly {
 
 /**
- * A Timekeeper with a dedicated thread that uses manages the timeouts using a
+ * A Timekeeper with a dedicated thread that manages the timeouts using a
  * heap. Timeouts can be scheduled with microsecond resolution, though in
  * practice the accuracy depends on the OS scheduler's ability to wake up the
  * worker thread in a timely fashion.