8326722: Cleanup unnecessary forward declaration in collectedHeap.hpp

Reviewed-by: tschatzl

Author: zhengyu123

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

@@ -46,9 +46,6 @@
 // class defines the functions that a heap must implement, and contains
 // infrastructure common to all heaps.
 
-class WorkerTask;
-class AdaptiveSizePolicy;
-class BarrierSet;
 class GCHeapLog;
 class GCHeapSummary;
 class GCTimer;