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

-------------
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);
 }
 

java/google/registry/util/Retrier.java

@@ -39,7 +39,7 @@ public class Retrier implements Serializable {
   private final int attempts;
 
   /** Holds functions to call whenever the code being retried fails. */
-  public static interface FailureReporter {
+  public interface FailureReporter {
 
     /**
      * Called after a retriable failure happened.
@@ -48,7 +48,7 @@ public class Retrier implements Serializable {
      *
      * <p>Not called at all if the retrier succeeded on its first attempt.
      */
-    public void beforeRetry(Throwable thrown, int failures, int maxAttempts);
+    void beforeRetry(Throwable thrown, int failures, int maxAttempts);
 
     /**
      * Called after a a non-retriable error.
@@ -58,7 +58,7 @@ public class Retrier implements Serializable {
      *
      * <p>Not called at all if the retrier succeeds.
      */
-    public void afterFinalFailure(Throwable thrown, int failures);
+    void afterFinalFailure(Throwable thrown, int failures);
   }
 
   @Inject

java/google/registry/util/TokenUtils.java

@@ -33,7 +33,7 @@ public final class TokenUtils {
     private final String prefix;
     private final int length;
 
-    private TokenType(String prefix, int length) {
+    TokenType(String prefix, int length) {
       this.prefix = prefix;
       this.length = length;
     }

java/google/registry/util/TypeUtils.java

@@ -101,7 +101,7 @@ public class TypeUtils {
   }
 
   /** Returns a predicate that tests whether classes are annotated with the given annotation. */
-  public static final Predicate<Class<?>> hasAnnotation(
+  public static Predicate<Class<?>> hasAnnotation(
       final Class<? extends Annotation> annotation) {
     return clazz -> clazz.isAnnotationPresent(annotation);
   }

java/google/registry/util/VoidCallable.java

@@ -25,7 +25,7 @@ public interface VoidCallable {
   void call() throws Exception;
 
   /** Returns the VoidCallable as a {@link Callable} that returns null. */
-  public default Callable<Void> asCallable() {
+  default Callable<Void> asCallable() {
     return () -> {
       call();
       return null;