Add generic XML syntax testing to a flow test

Adding it to one test is sufficient because we use the same loading logic across all flows.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=239506003

javatests/google/registry/flows/FlowTestCase.java

@@ -226,13 +226,6 @@ public abstract class FlowTestCase<F extends Flow> extends ShardableTestCase {
     assertPollMessagesHelper(getPollMessages(clientId), expected);
   }
 
-  public void assertPollMessages(
-      String clientId,
-      DateTime now,
-      PollMessage... expected) {
-    assertPollMessagesHelper(getPollMessages(clientId, now), expected);
-  }
-
   public void assertPollMessages(PollMessage... expected) {
     assertPollMessagesHelper(getPollMessages(), expected);
   }
@@ -326,10 +319,6 @@ public abstract class FlowTestCase<F extends Flow> extends ShardableTestCase {
 
   private TmchCaMode tmchCaMode = TmchCaMode.PILOT;
 
-  protected void useTmchProdCert() {
-    tmchCaMode = TmchCaMode.PRODUCTION;
-  }
-
   public EppOutput dryRunFlowAssertResponse(String xml, String... ignoredPaths) throws Exception {
     List<Object> beforeEntities = ofy().load().list();
     EppOutput output =