Fix all uses of DateTime.now() to use DateTimeZone.UTC

Almost all uses were in test classes, which I replaced with clock.nowUTC().

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=134993149

javatests/google/registry/flows/domain/DomainApplicationInfoFlowTest.java

@@ -274,7 +274,7 @@ public class DomainApplicationInfoFlowTest
     persistResource(new DomainApplication.Builder()
         .setRepoId("123-COM")
         .setFullyQualifiedDomainName("timber.com")
-        .setDeletionTime(DateTime.now().minusDays(1))
+        .setDeletionTime(clock.nowUtc().minusDays(1))
         .setRegistrant(Key.create(persistActiveContact("jd1234")))
         .build());
     runFlow();