Redirect Registrar.referralUrl UI actions to url field

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=196597051

javatests/google/registry/testing/FullFieldsTestEntityHelper.java

@@ -80,7 +80,6 @@ public final class FullFieldsTestEntityHelper {
       .setFaxNumber("+1.2125551213")
       .setEmailAddress("contact-us@example.com")
       .setWhoisServer("whois.example.com")
-      .setReferralUrl("http://www.example.com")
       .setUrl("http://my.fake.url")
       .build();
   }