libobs:  Fix switch warning
UI: Remove unused variable
CoreAudio: Enumerate AudioDeviceID manually

Apparently, despite the fact that Apple added
kAudioHardwarePropertyTranslateUIDToDevice in 10.8, it's not actually
usable in 10.8, only 10.9.  So, instead of being able to use it like a
normal, sane person, we have to enumerate all devices manually and find
the AudioDeviceID ourselves.  A slight annoyance and a mark against
apple's competence, but audio devices should now be working again on
10.8 at least, so whatever.