Remove uses of UseWebBasedSigninFlow().

      Chrome no longer supports the non web-based sign in flow, so removing the
flag that controls it and code that executed for that flow.  This is the
first CL of several to completely remove non web-based sign in flow support.

BUG=92948

Review URL: https://chromiumcodereview.appspot.com/14685005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@204694 0039d316-1c4b-4281-b951-d872f2087c98