AudioStream: Swap to shared soundtouch library

Yay licensing requirements.

src/util/audio_stream.h

@@ -279,7 +279,7 @@ private:
   std::atomic<u32> m_rpos{0};
   std::atomic<u32> m_wpos{0};
 
-  std::unique_ptr<soundtouch::SoundTouch> m_soundtouch;
+  void* m_soundtouch = nullptr;
 
   u32 m_target_buffer_size = 0;
   u32 m_stretch_reset = STRETCH_RESET_THRESHOLD;