8302072: Parallel: Remove unimplemented ParCompactionManager::stack_push

Reviewed-by: tschatzl

src/hotspot/share/gc/parallel/psCompactionManager.hpp

@@ -110,12 +110,6 @@ class ParCompactionManager : public CHeapObj<mtGC> {
   static RegionTaskQueueSet* region_task_queues()      { return _region_task_queues; }
   OopTaskQueue*  oop_stack()       { return &_oop_stack; }
 
-  // Pushes onto the marking stack.  If the marking stack is full,
-  // pushes onto the overflow stack.
-  void stack_push(oop obj);
-  // Do not implement an equivalent stack_pop.  Deal with the
-  // marking stack and overflow stack directly.
-
  public:
   static const size_t InvalidShadow = ~0;
   static size_t  pop_shadow_region_mt_safe(PSParallelCompact::RegionData* region_ptr);