Add device reference counting

src/backend/null/NullBackend.cpp

@@ -101,12 +101,6 @@ namespace null {
         return std::move(pendingOperations);
     }
 
-    void Device::Reference() {
-    }
-
-    void Device::Release() {
-    }
-
     // Buffer
 
     struct BufferMapReadOperation : PendingOperation {

src/backend/null/NullBackend.h

@@ -112,10 +112,6 @@ namespace null {
             void AddPendingOperation(std::unique_ptr<PendingOperation> operation);
             std::vector<std::unique_ptr<PendingOperation>> AcquirePendingOperations();
 
-            // NXT API
-            void Reference();
-            void Release();
-
         private:
             std::vector<std::unique_ptr<PendingOperation>> pendingOperations;
     };