Avoid the test frame for DXVA2 and VT APIs to address flickering in full-screen on Win7

app/streaming/video/ffmpeg-renderers/vaapi.h

@@ -37,6 +37,7 @@ public:
                             int maxFps);
     virtual bool prepareDecoderContext(AVCodecContext* context);
     virtual void renderFrameAtVsync(AVFrame* frame);
+    virtual bool needsTestFrame();
 
 private:
     int m_WindowSystem;