Avoid doubly penalizing rescheduled periodic jobs for flex.

Periodic jobs that were completed successfully and rescheduled sometimes
have adjusted start times to avoid running them back to back. When this
happens, make sure the flex logic takes the adjustment into account and
doesn't delay the constraint drops too significantly.

Bug: 236261941
Test: atest FrameworksMockingServicesTests:FlexibilityControllerTest
Change-Id: I039f86a409754089c7592719e0fd3355d6883cfb