PulseAudio: preserve audio format, fix some races, simplify and cleanup

 - preserve sample format from VLC, if possible,
 - preserve physical channels mapping,
 - remove a useless callback,
 - fix small race conditions with pa_*_wait() on startup,
 - cosmetic changes.
(cherry picked from commit 176927134d1d82836f7a545cf5cc3a19a842a8d6)
(cherry picked from commit a6274616f21886a1b025c62ac0bca30b165d3db8)
(cherry picked from commit 90ef491bb4fa4b93b4bc620f656828ad47f0d8a7)

Conflicts:

	modules/audio_output/pulse.c