Always restore staged sessions on boot.

The current logic doesn't restore sessions unless they are "in flight".
We want staged session to stick around until they expire after
MAX_TIME_SINCE_UPDATE_MILLIS.

Bug: 131290871
Test: atest CtsStagedInstallHostTestCases (with modifications coming in
a separate CL)

Change-Id: Ifaccf50e744a97e30a4fda0e47b88d7dc71adcf8