Revert of Implement async AbortAll for the compiler dispatcher

src/cancelable-task.h

Index: src/cancelable-task.h
diff --git a/src/cancelable-task.h b/src/cancelable-task.h
index 04f775cbe8d7668df2bcc794cde66e7c7c9d8cb9..578db6f6b997c624a0c3a7af901978f6fd534de7 100644
--- a/src/cancelable-task.h
+++ b/src/cancelable-task.h
@@ -44,17 +44,6 @@
   // Cancels all remaining registered tasks and waits for tasks that are
   // already running. This disallows subsequent Register calls.
   void CancelAndWait();
-
-  // Tries to cancel all remaining registered tasks. The return value indicates
-  // whether
-  //
-  // 1) No tasks were registered (kTaskRemoved), or
-  //
-  // 2) There is at least one remaining task that couldn't be cancelled
-  // (kTaskRunning), or
-  //
-  // 3) All registered tasks were cancelled (kTaskAborted).
-  TryAbortResult TryAbortAll();
 
  private:
   // Only called by {Cancelable} destructor. The task is done with executing,