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

javatests/google/registry/whois/WhoisReaderTest.java

@@ -47,7 +47,7 @@ public class WhoisReaderTest {
     WhoisReader.logger.addHandler(testLogHandler);
   }
 
-  @SuppressWarnings("TypeParameterUnusedInFormals") // XXX: Generic abuse ftw.
+  @SuppressWarnings({"TypeParameterUnusedInFormals", "unchecked"})
   <T> T readCommand(String commandStr) throws Exception {
     return (T)
         new WhoisReader(new WhoisCommandFactory())