Remove linkToDeath from KeyguardUnlockAnimationController.

This results in leaking the NexusLauncherActivity, and
should not be necessary as we check for DeadObjectExceptions
already.

Fixes: 221892011
Test: kill sysui/launcher in different orders, things still work fine
Change-Id: I8c86d37db602003f272b701f8d03724f21a7a930