Avoid using stale sessions for cleanup alarm.

Remove old EJ timing sessions before we schedule the next cleanup alarm.
If we don't remove them, then we will continue to use stale sessions as
the basis for the next cleanup alarm, which would eventually result in
scheduling alarms in the past.

Bug: 187351354
Test: atest FrameworksMockingServicesTest:QuotaControllerTest
Change-Id: I1b968e0461efe9aad3e785760a3cd2f5d8d4de8b