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/util/RequestStatusChecker.java

@@ -24,11 +24,11 @@ public interface RequestStatusChecker extends Serializable {
    *
    * <p>Multiple calls must return the same value during the same Request.
    */
-  public String getLogId();
+  String getLogId();
 
   /**
    * Returns true if the given request is currently running.
    */
-  public boolean isRunning(String requestLogId);
+  boolean isRunning(String requestLogId);
 }