Remove unlock dialog from sysui

Bug: 153104923
Test: m -j CarSystemUI && adb sync && adb shell pkill systemui
      Manually tested:
      1) Boot with no security;
      2) Boot with security and unlock;
      3) Boot with security, cancel unlock and switch to user with
      security;
      4) Boot with security, cancel unlock and switch to user without
      security.

Change-Id: Id8f13db3d5b53ffd6b3d8624ea2e3f51982b4910