Fix "Request to restore userData ..." log spam.

We shouldn't be logging an error message if no rollback data is
available for a package in restoreUserData, because that function is
called regularly with applications that don't have rollback enabled.

Bug: 125768945
Test: atest RollbackTest ; adb logcat -d | grep RollbackManager
Change-Id: I908cbbefb6efbc1b4f0dd81500914616e502a7fb