Revert of Use background tasks 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 578db6f6b997c624a0c3a7af901978f6fd534de7..65f98e766287dea41bb89ec2f1e02cdc65242df4 100644
--- a/src/cancelable-task.h
+++ b/src/cancelable-task.h
@@ -126,7 +126,6 @@
 class CancelableTask : public Cancelable, public Task {
  public:
   explicit CancelableTask(Isolate* isolate);
-  CancelableTask(Isolate* isolate, CancelableTaskManager* manager);
 
   // Task overrides.
   void Run() final {
@@ -149,7 +148,6 @@
 class CancelableIdleTask : public Cancelable, public IdleTask {
  public:
   explicit CancelableIdleTask(Isolate* isolate);
-  CancelableIdleTask(Isolate* isolate, CancelableTaskManager* manager);
 
   // IdleTask overrides.
   void Run(double deadline_in_seconds) final {