change: Remove dropped "audiohost" from advancedsettings

According to IRC talk

XMLUtils::GetString(pElement, "audiohost", m_audioHost);

Is left over and gone.
also remove references in https://github.com/xbmc/xbmc/blob/cff55a425ad8a610c3781b66ba75a0102d014fe4/xbmc/settings/AdvancedSettings.h#L180
and 
https://github.com/xbmc/xbmc/blob/6afb499a211a0e3ebd9473a3a1425eebebb67c3f/xbmc/settings/AdvancedSettings.cpp#L130

tbh I bit off more than I can chew but at least its here for reference if nothing else right?

@fritsch