Attempt install-time restore even for no-agent apps

Packages without their own backup agents can still have restorable
data to be delivered.  Correct the logic for attempting a restore
at install time so that it no longer requires an app-defined backup
agent.

Bug 16688665

Change-Id: I7dcf7ef85ad6b5b393a2c97ce62f1b2eec9d3520