cleanup: remove PortAudio support
cleanup: remove PortAudio support

This was discussed in some of the earlier commits. PortAudio doesn't give any real advantages over libao and libao is at least as portable as PortAudio. And we should try to keep the code clean.

hendrikw82/shairport,bowlofstew/shairport,mspasov/shairport,IronBeard/shairport,dotmpe/shairport,albertz/shairport,skaman/shairport,bowlofstew/shairport,hendrikw82/shairport,skaman/shairport,dotmpe/shairport,IronBeard/shairport,hendrikw82/shairport,narakai/shairport,IronBeard/shairport,dotmpe/shairport,narakai/shairport,bowlofstew/shairport,mspasov/shairport,narakai/shairport,albertz/shairport