Fix checkstyle violations

Author: snicoll

spring-core/src/main/java/org/springframework/util/unit/DataSize.java

@@ -31,7 +31,7 @@
  * @author Stephane Nicoll
  * @since 5.1
  */
-public class DataSize implements Comparable<DataSize> {
+public final class DataSize implements Comparable<DataSize> {
 
 	/**
 	 * The pattern for parsing.

spring-core/src/main/java/org/springframework/util/unit/package-info.java

@@ -1,19 +1,3 @@
-/*
- * Copyright 2002-2018 the original author or authors.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
 /**
  * Useful unit data types.
  */
@@ -22,4 +6,4 @@
 package org.springframework.util.unit;
 
 import org.springframework.lang.NonNullApi;
-import org.springframework.lang.NonNullFields;
+import org.springframework.lang.NonNullFields;