Revert "Convert assumption to conditional in freezer test"

Now that http://b/148899617 is fixed, and after leaving test
infrastructure some time to update to ag/10254650, it's time to revert
this workaround.

Bug: 148899617
Test: atest com.android.server.am.CachedAppOptimizerTest
Test: atest FrameworksMockingServicesTests:StaticMockFixtureRuleTest
This reverts commit f0962a49.