Disabling exact alarm permission enforcement

Disabling the CompatChange id for changing the default behavior of
SCHEDULE_EXACT_ALARM.
Removing the corresponding device_config flag as it doesn't matter with
the change id disabled.
Rest of the underlying code is kept in a working state to be testable.

Test: atest CtsAlarmManagerTestCases
atest FrameworksMockingServicesTests:AlarmManagerServiceTest

Bug: 226439802
Bug: 231661074
Change-Id: Ifff8f8ad4721868d33b7b8e201bc1411e3a7cab2