Clean up some code quality issues

This removes some qualifiers that aren't necessary (e.g. public/abstract on interfaces, private on enum constructors, final on private methods, static on nested interfaces/enums), uses Java 8 lambdas and features where that's an improvement

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=177182945

java/google/registry/model/domain/DomainCommand.java

@@ -67,7 +67,7 @@ public class DomainCommand {
    */
   public interface CreateOrUpdate<T extends CreateOrUpdate<T>> extends SingleResourceCommand {
     /** Creates a copy of this command with hard links to hosts and contacts. */
-    public T cloneAndLinkReferences(DateTime now) throws InvalidReferencesException;
+    T cloneAndLinkReferences(DateTime now) throws InvalidReferencesException;
   }
 
   /** The fields on "chgType" from {@link "http://tools.ietf.org/html/rfc5731"}. */