Schedule sqlite writes into the registry

XML registry takes signal from AppOpsService for
writing the data to disk on regular interval,
the scheduling is happening in AppOpsService.
I believe the registry should schedule its write
itself, and AppOpsService doesn't need know about
scheduling of writes in this registry.

Bug: 377584611
Test: manual
Test: atest com.android.server.appop.DiscreteOpsMigrationAndRollbackTest
Test: atest com.android.server.appop.DiscreteAppOpSqlPersistenceTest
FLAG: EXEMPT bug fix
Change-Id: I85d9a576a88ff6cd8c2c7794d0d06c2ffa11a07e