login: Fix StopArcInstance There was a stray dbus command in StopArcInstance that caused it to crash. BUG=b:24339743 TEST=StopArcInstance no longer crashes. Change-Id: I1c918fa7bbabcb19e124a48cfdfd42ffbf1dfb5b Reviewed-on: https://chromium-review.googlesource.com/311416 Commit-Ready: Luis Hector Chavez <lhchavez@google.com> Tested-by: Luis Hector Chavez <lhchavez@google.com> Reviewed-by: Dan Erat <derat@chromium.org>