Move AudioOutput back to inside audio processor classes.

Was wasting precious RAM making it static. I lose 400 bytes of .text, not sure why, but I think the trade is worth it.

firmware/baseband/audio_output.cpp

@@ -98,5 +98,3 @@ void AudioOutput::feed_audio_stats(const buffer_f32_t& audio) {
 		}
 	);
 }
-
-AudioOutput audio_output;