UI: Fix advanced audio properties duplication bug

Because of the patch that removed the "user sources list" in libobs
(70fec7ae8), obs_enum_sources will now enumerate the global audio
sources, where it didn't before.  In the advanced audio properties
dialog, before the patch I had to use code to manually include them, but
I neglected to remove that code when I made that patch, so it would
cause them to be added more than once.  This just removes that code.

obs/window-basic-adv-audio.cpp

@@ -66,15 +66,6 @@ OBSBasicAdvAudio::OBSBasicAdvAudio(QWidget *parent)
 
 	installEventFilter(CreateShortcutFilter());
 
-	/* get global audio sources */
-	for (uint32_t i = 1; i <= 10; i++) {
-		obs_source_t *source = obs_get_output_source(i);
-		if (source) {
-			AddAudioSource(source);
-			obs_source_release(source);
-		}
-	}
-
 	/* enum user scene/sources */
 	obs_enum_sources(EnumSources, this);