Fix accidental enrollment auth reset callback duplication.

This causes the auth reset callback to be triggered twice, which
results in to WizardController::OnEnrollmentDone() invocations, which
breaks Kiosk App launch after enrollment.

BUG=chromium:295815
TEST=Kiosk App launch after enrollment consistently succeeds.
R=joaodasilva@chromium.org, nkostylev@chromium.org

Review URL: https://codereview.chromium.org/24358009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225165 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225165