Improve ListDomainsCommand to list domains on multiple TLDs

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=140053423

javatests/google/registry/tools/ListHostsCommandTest.java

@@ -27,9 +27,4 @@ public class ListHostsCommandTest extends ListObjectsCommandTestCase<ListHostsCo
   final String getTaskPath() {
     return ListHostsAction.PATH;
   }
-
-  @Override
-  final String getTld() {
-    return null;
-  }
 }