[Files.app] Remove the support of overriding the CWS widget container URL.

The CWS widget container is already on prod so we don't need to override it anymore.

BUG=none
TEST=manual
R=hirono@chromium.org

Review URL: https://codereview.chromium.org/24270005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224856 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224856