Inject clock for Tmch validity using InjectRule instead of manually

Basically a less patchy version of []

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=202138086

javatests/google/registry/flows/EppLifecycleDomainTest.java

@@ -45,7 +45,6 @@ import google.registry.model.registry.Registry;
 import google.registry.model.registry.Registry.TldState;
 import google.registry.model.reporting.HistoryEntry.Type;
 import google.registry.testing.AppEngineRule;
-import google.registry.tmch.TmchCertificateAuthority;
 import java.util.Objects;
 import java.util.Optional;
 import org.joda.money.Money;
@@ -66,8 +65,6 @@ public class EppLifecycleDomainTest extends EppTestCase {
 
   @Before
   public void initTld() {
-    // Setting the clock used for SignedMark signature validity.
-    TmchCertificateAuthority.clock = () -> DateTime.parse("2015-01-01TZ");
     createTlds("example", "tld");
   }