Properly handle disabled location prefetch.

The controller was still registering for location updates when location
prefetch was disabled. Now, it skips requesting location updates
altogether when location prefetch is disabled.

Bug: 279725615
Test: atest DeviceIdleTest
Test: atest FrameworksMockingServicesTests:DeviceIdleControllerTest
Change-Id: If303d5448acbc4e97132f3713a7795e46eacc5ab