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 f0962a49d2.

services/tests/mockingservicestests/src/com/android/server/am/CachedAppOptimizerTest.java

@@ -36,6 +36,7 @@ import com.android.server.appop.AppOpsService;
 import com.android.server.testables.TestableDeviceConfig;
 
 import org.junit.After;
+import org.junit.Assume;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
@@ -267,9 +268,7 @@ public final class CachedAppOptimizerTest {
 
     @Test
     public void useFreeze_doesNotListenToDeviceConfigChanges() throws InterruptedException {
-        if (!mCachedAppOptimizerUnderTest.isFreezerSupported()) {
-            return;
-        }
+        Assume.assumeTrue(mCachedAppOptimizerUnderTest.isFreezerSupported());
 
         assertThat(mCachedAppOptimizerUnderTest.useFreezer()).isEqualTo(
                 CachedAppOptimizer.DEFAULT_USE_FREEZER);