audio: don't use a shared QIODevice

This system was kind of janky anyway. It makes more sense ultimately for the
audio management classes to contain the file handle rather than the renderer.

app/render/backend/audio/audiobackend.cpp

@@ -34,13 +34,6 @@ AudioBackend::~AudioBackend()
   Close();
 }
 
-QIODevice *AudioBackend::GetAudioPullDevice()
-{
-  pull_device_.setFileName(CachePathName());
-
-  return &pull_device_;
-}
-
 bool AudioBackend::InitInternal()
 {
   // Initiate one thread per CPU core

app/render/backend/audio/audiobackend.h

@@ -35,8 +35,6 @@ public:
 
   virtual ~AudioBackend() override;
 
-  virtual QIODevice* GetAudioPullDevice() override;
-
 protected:
   virtual bool InitInternal() override;
 
@@ -51,9 +49,6 @@ protected:
 private slots:
   void ThreadCompletedCache(NodeDependency dep, NodeValueTable data, qint64 job_time);
 
-private:
-  QFile pull_device_;
-
 };
 
 OLIVE_NAMESPACE_EXIT

app/render/backend/audiorenderbackend.h

@@ -40,8 +40,6 @@ public:
    */
   void SetParameters(const AudioRenderingParams &params);
 
-  virtual QIODevice* GetAudioPullDevice() = 0;
-
   const AudioRenderingParams& params() const;
 
   QString CachePathName() const;