Revert 244098 "Fix chromeos=1 so Pulse is preferred when use_cra..."

Speculative revert to fix link errors on ChromiumOS amd64 BuildPackages,
complaining about undefined reference to 'alsa_util::BitsToFormat(int)'.

> Fix chromeos=1 so Pulse is preferred when use_cras=0.
> 
> Merges the settings for use_alsa and use_pulseaudio for selection
> based on use_cras.
> 
> BUG=none
> TEST=Pulse is available along with ALSA when chromeos=1.
> 
> Review URL: https://codereview.chromium.org/132773002

TBR=dalecurtis@chromium.org

Review URL: https://codereview.chromium.org/131063006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244100 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244100