ao_alsa: print channel map if setting it fails

This message is printed when the audio device advertised a channel map,
but couldn't set it - which is probably a dmix bug (we'll never know,
ALSA doesn't take bug reports).

Print the requested map, so that the user (maybe) can make a connection
when seeing the message and the actually used channel map, which might
be less confusing. Or at least less useless.
ao_portaudio: remove this audio output

It's just completely useless. We have good native support for all 3
desktop platforms, and ao_sdl or ao_openal as fallbacks.