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/xjc/JaxbFragment.java

@@ -57,7 +57,7 @@ public class JaxbFragment<T> implements Serializable {
   }
 
   /** Deserializes a JAXB element from xml bytes. */
-  private static <T> T unfreezeInstance(byte[] instanceData, Class<? extends Object> instanceType)
+  private static <T> T unfreezeInstance(byte[] instanceData, Class<?> instanceType)
       throws IOException {
     try {
       ByteArrayInputStream bin = new ByteArrayInputStream(instanceData);