Don't discard all excess frames before rendering

This prevents the render queue's pacing logic from working and
interferes with renderers that take a full v-sync period between
their waitToRender() and renderFrame() callbacks.

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

@@ -33,8 +33,6 @@ private:
 
     void enqueueFrameForRenderingAndUnlock(AVFrame* frame);
 
-    void renderLastFrameAndUnlock();
-
     void renderFrame(AVFrame* frame);
 
     void dropFrameForEnqueue(QQueue<AVFrame*>& queue);