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/EscrowTaskRunner.java

@@ -61,7 +61,7 @@ class EscrowTaskRunner {
      *
      * @param watermark the logical time for a point-in-time view of Datastore
      */
-    abstract void runWithLock(DateTime watermark) throws Exception;
+    void runWithLock(DateTime watermark) throws Exception;
   }
 
   private static final FormattingLogger logger = FormattingLogger.getLoggerForCallerClass();