Updated License dates to 2016

Several files had 2017 dates for License. Checkstyle now specifically
looks for 2016 date in License comments.

Author: benjamintboyle

HEADER_JAVA

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-present, RxJava Contributors.
+ * Copyright (c) 2016-present, RxJava Contributors.
  *
  * 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
@@ -9,4 +9,4 @@
  * 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.
- */
+ */

checkstyle.xml

@@ -8,13 +8,6 @@
     <!-- Headers -->
     <module name="Header">
         <property name="headerFile" value="${checkstyle.header.file}"/>
-        <!-- Ignores date line, which is checked in RegexpHeader module below -->
-        <property name="ignoreLines" value="2"/>
-        <property name="fileExtensions" value="java"/>
-    </module>
-    <!-- Checks Line 2 of Copyright Header -->
-    <module name="RegexpHeader">
-        <property name="header" value="^/*\n * Copyright \(c\) \d{4}-present, RxJava Contributors\.$"/>
         <property name="fileExtensions" value="java"/>
     </module>
 

src/test/java/io/reactivex/rxjava3/completable/CompletableRetryTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-present, RxJava Contributors.
+ * Copyright (c) 2016-present, RxJava Contributors.
  *
  * 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

src/test/java/io/reactivex/rxjava3/maybe/MaybeRetryTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-present, RxJava Contributors.
+ * Copyright (c) 2016-present, RxJava Contributors.
  *
  * 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

src/test/java/io/reactivex/rxjava3/single/SingleRetryTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-present, RxJava Contributors.
+ * Copyright (c) 2016-present, RxJava Contributors.
  *
  * 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

src/test/java/io/reactivex/rxjava3/validators/FixLicenseHeaders.java

@@ -1,4 +1,4 @@
-/**
+/*
  * Copyright (c) 2016-present, RxJava Contributors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in