Fix timer bug in TrustManagerService.

Previously, anytime a device was unlocked, we would refresh the trustable timers. Now, we should ensure that there actually is a trustable timer running before refreshing (since updating trust will start it anyways). We also make sure to destroy the timers when we move to UNTRUSTED

Fixes:273550297
Fixes:264684930
Change-Id: I75d58e09848d4123bb55ea9a36cab739504ca6e8
Test: Tested that this fixes 273550297 by justinkchung@