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/batch/DeleteContactsAndHostsAction.java

@@ -536,7 +536,7 @@ public class DeleteContactsAndHostsAction implements Runnable {
       private final String counterFormat;
       private final OperationResult operationResult;
 
-      private Type(String counterFormat, OperationResult operationResult) {
+      Type(String counterFormat, OperationResult operationResult) {
         this.counterFormat = counterFormat;
         this.operationResult = operationResult;
       }