Revert d3c49be80f and do it better

Source/Engine/Graphics/Async/GPUTask.h

@@ -58,8 +58,6 @@ protected:
     {
     }
 
-    ~GPUTask();
-
 public:
     /// <summary>
     /// Gets a task type.
@@ -142,24 +140,5 @@ protected:
         return true;
     }
 
-    void OnCancel() override
-    {
-        // Check if task is waiting for sync (very likely situation)
-        if (IsSyncing())
-        {
-            // Task has been performed but is waiting for a CPU/GPU sync so we have to cancel that
-            ASSERT(_context != nullptr);
-            _context->OnCancelSync(this);
-            _context = nullptr;
-            SetState(TaskState::Canceled);
-        }
-        else
-        {
-            // Maybe we could also handle cancel event during running but not yet syncing
-            ASSERT(!IsRunning());
-        }
-
-        // Base
-        Task::OnCancel();
-    }
+    void OnCancel() override;
 };