www/chromium: unbreak WebRTC microphone selection with PULSEAUDIO=off

Similar to r414386. No kernel ALSA is available to enumerate soundcards,
so assume sound(4) can always be used via ALSA plugins like "oss".
This partially reverts https://codereview.chromium.org/7888011/

PR: 206480
Reported by: Betso <betso.net@gmail.com>
Reviewed by: cem, cmt (briefly)
Approved by: maintainer timeout (2 weeks)
MFH: 2016Q2