libobs: Rename obs_audio_monitoring_supported to _available

With the reasonable possibility of monitoring support becoming a
runtime check, the phrase `available` is more fitting.

UI/window-basic-main-profiles.cpp

@@ -492,7 +492,7 @@ void OBSBasic::ResetProfileData()
 	CreateHotkeys();
 
 	/* load audio monitoring */
-	if (obs_audio_monitoring_supported()) {
+	if (obs_audio_monitoring_available()) {
 		const char *device_name = config_get_string(
 			basicConfig, "Audio", "MonitoringDeviceName");
 		const char *device_id = config_get_string(basicConfig, "Audio",