Move audio capabilities out of the renderer classes

Since the removal of libsoundio, all renderers support arbitrary audio duration, so we can avoid having to start an audio session just to query capabilities.

app/streaming/audio/renderers/slaud.cpp

@@ -114,11 +114,6 @@ bool SLAudioRenderer::submitAudio(int bytesWritten)
     return true;
 }
 
-int SLAudioRenderer::getCapabilities()
-{
-    return CAPABILITY_SLOW_OPUS_DECODER | CAPABILITY_SUPPORTS_ARBITRARY_AUDIO_DURATION;
-}
-
 IAudioRenderer::AudioFormat SLAudioRenderer::getAudioBufferFormat()
 {
     return AudioFormat::Sint16NE;