Use JobScheduler's storage-not-low constraint.

Switch to using JobScheduler's storage-not-low constraint instead of
doing it inside of SyncManager. SyncManager used to handle the
constraint before JobScheduler existed and the code wasn't updated to
use the new constraint.

Bug: 185949373
Test: atest ContentResolverTest (all)
Test: atest CtsSyncManagerTest
Test: atest SyncOperationTest
Test: atest SyncManagerTest
Test: atest SyncRequestTest
Change-Id: I06b26388e50641e1233ce727693eab18b74066b2