8343929: Remove PreservedMarksSet::createTask() after JDK-8305895

Reviewed-by: ayang, shade

src/hotspot/share/gc/shared/preservedMarks.cpp

@@ -143,10 +143,6 @@ void PreservedMarksSet::restore(WorkerThreads* workers) {
   assert_empty();
 }
 
-WorkerTask* PreservedMarksSet::create_task() {
-  return new RestorePreservedMarksTask(this);
-}
-
 void PreservedMarksSet::reclaim() {
   assert_empty();
 

src/hotspot/share/gc/shared/preservedMarks.hpp

@@ -114,8 +114,6 @@ public:
   // is null, perform the work serially in the current thread.
   void restore(WorkerThreads* workers);
 
-  WorkerTask* create_task();
-
   // Reclaim stack array.
   void reclaim();