Switch from volatile to lock.

The shell command handling method was the only place
mDeterministicUidIdle was being accessed without a lock already being
held on ActivityManagerService, so switch to just requiring the lock on
the boolean instead of making it volatile.

Bug: 286700610
Test: atest CtsJobSchedulerTestCases:JobThrottlingTest
Test: atest CtsJobSchedulerTestCases:NotificationTest
Test: atest CtsJobSchedulerTestCases:UserInitiatedJobTest
Test: atest FrameworksMockingServicesTests:JobNotificationCoordinatorTest
Test: atest FrameworksMockingServicesTests:MockingOomAdjusterTests
Test: atest FrameworksServicesTests:OomAdjusterTests
Change-Id: I6945cc9b4cda8cd19e876de4b19e0f0a6f6a782e