Update #registerAppUsageLimitObserver to take time used.

Update the time remaining parameter of #registerAppUsageLimitObserver to
time used to avoid confusion between time limit and time remaining.

Bug: 128414428
Test: atest FrameworksServicesTests:AppTimeLimitControllerTests
Test: atest android.app.usage.cts.UsageStatsTest#testObserveUsagePermissionForRegisterObserver
Test: atest android.app.usage.cts.UsageStatsTest#testObserveUsagePermissionForUnregisterObserver
Test: manual (mmma frameworks/base/tests/UsageStatsTest/)
Change-Id: Ied8e4ca0b8636bb9efc4d85dcae46ac6cf1ef5f7