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/tools/LevelDbUtil.java

@@ -81,9 +81,7 @@ class LevelDbUtil {
     pos = addRecordHeader(bytes, pos, type, data.length);
 
     // Write the contents of "data".
-    for (int i = 0; i < data.length; ++i) {
-      bytes[pos + i] = data[i];
-    }
+    System.arraycopy(data, 0, bytes, pos, data.length);
 
     return pos + data.length;
   }