Remove use of CoreAudioUtil::IsSupported() from AudioManager startup.

The method attempts to load the audioses.dll and create an
MMDeviceEnumerator object.  Such actions should be avoided in the
constructor since it's blocking the UI loop.

BUG=none
TEST=none

Review URL: https://codereview.chromium.org/144613003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246527 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246527