Fix license on AcitveDirectorySIDUtil (#30972)

This code is from an Apache 2.0 licensed codebase and when we imported
it into our codebase it carried the Apache 2.0 license as well. However,
during the migration of the X-Pack codebase from the internal private
repository to the elastic/elasticsearch repository, the migration tool
mistakently changed the license on this source file from the Apache 2.0
license to the Elastic license. This commit addresses this mistake by
reapplying the Apache 2.0 license.

x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authc/ldap/ActiveDirectorySIDUtil.java

@@ -1,7 +1,20 @@
 /*
- * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
- * or more contributor license agreements. Licensed under the Elastic License;
- * you may not use this file except in compliance with the Elastic License.
+ *  Licensed to the Apache Software Foundation (ASF) under one
+ *  or more contributor license agreements.  See the NOTICE file
+ *  distributed with this work for additional information
+ *  regarding copyright ownership.  The ASF licenses this file
+ *  to you 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.
  */
 
 /*