Redirect Registrar.referralUrl UI actions to url field

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

java/google/registry/ui/server/RegistrarFormFields.java

@@ -154,10 +154,6 @@ public final class RegistrarFormFields {
       FormFields.MIN_TOKEN.asBuilderNamed("url")
           .build();
 
-  public static final FormField<String, String> REFERRAL_URL_FIELD =
-      FormFields.MIN_TOKEN.asBuilderNamed("referralUrl")
-          .build();
-
   public static final FormField<List<String>, List<CidrAddressBlock>> IP_ADDRESS_WHITELIST_FIELD =
       FormField.named("ipAddressWhitelist")
           .emptyToNull()

java/google/registry/ui/server/registrar/RegistrarSettingsAction.java

@@ -224,8 +224,7 @@ public class RegistrarSettingsAction implements Runnable, JsonActionRunner.JsonA
     // WHOIS
     builder.setWhoisServer(
         RegistrarFormFields.WHOIS_SERVER_FIELD.extractUntyped(args).orElse(null));
-    builder.setReferralUrl(
-        RegistrarFormFields.REFERRAL_URL_FIELD.extractUntyped(args).orElse(null));
+    builder.setUrl(RegistrarFormFields.URL_FIELD.extractUntyped(args).orElse(null));
 
     // If the email is already null / empty - we can keep it so. But if it's set - it's required to
     // remain set.
@@ -241,8 +240,6 @@ public class RegistrarSettingsAction implements Runnable, JsonActionRunner.JsonA
     builder.setLocalizedAddress(
         RegistrarFormFields.L10N_ADDRESS_FIELD.extractUntyped(args).orElse(null));
 
-    builder.setUrl(RegistrarFormFields.URL_FIELD.extractUntyped(args).orElse(null));
-
     // Security
     builder.setIpAddressWhitelist(
         RegistrarFormFields.IP_ADDRESS_WHITELIST_FIELD