SystemUI: fix crypt keeper race condition

We check package manager whether crypt keeper has disabled itself, but
if crypt keeper is in the process of disabling itself, the lockscreen
might get in a bad state.

Instead of checking package manager, let's use the same check that
CryptKeeper uses to decide whether to disable itself.

Change-Id: I9de09a1248b28fa14db9f69fb1313778895e2438
Signed-off-by: Roman Birg <roman@cyngn.com>