Update Deskclock to use USE_EXACT_ALARM

Since API 33, DeskClock can use USE_EXACT_ALARM permission to use exact
alarms.

Keeping SCHEDULE_EXACT_ALARM declared for previous versions.

Test: Manual. Build and install app on Build with version > 32.
Verify that the app doesn't show up in Settings -> Apps -> Special app
-> Alarms and Reminders
Verify that the basic functionality in the app works as expected.

Bug: 218533173
Change-Id: I039aa8009f5ae5489df2b9beb43de8566ced846d