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/rde/imports/RdeParser.java

@@ -198,8 +198,7 @@ public class RdeParser implements Closeable {
     checkArgumentNotNull(uri, "uri cannot be null");
     try {
       if (isAtElement(uri, name)) {
-        Object element = unmarshaller.unmarshal(reader);
-        return element;
+        return unmarshaller.unmarshal(reader);
       } else {
         throw new IllegalStateException(String.format("Not at element %s:%s", uri, name));
       }