Remove regtype extension since we won't be using it

If we do end up needing it we can simply revert this commit.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=127094676

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

@@ -1282,13 +1282,6 @@ public class DomainCreateFlowTest extends ResourceFlowTestCase<DomainCreateFlow,
     doSuccessfulTest();
   }
 
-  @Test
-  public void testSuccess_regTypeExtensionValidates() throws Exception {
-    setEppInput("domain_create_regtype.xml");
-    persistContactsAndHosts();
-    doSuccessfulTest("tld", "domain_create_response.xml");
-  }
-
   @Test
   public void testSuccess_eapFeeApplied() throws Exception {
     setEppInput("domain_create_eap_fee.xml");