Fix idle maintenance wrt checkpoint check

By calling out to needsCheckpoint and supportsBlockCheckpoint, we
inadvertently added the need for system permission to idleMain.
Relax these permissions.

Test: sm idle-maint run fails without this change, passes with
Bug: 131680526
Change-Id: I3202ca5d818a90d72cce8cdb2c634b21ba308715
(cherry picked from commit eb4f12ca)