ARROW-6812: [Java] Fix License header

Remove Dremio Corporation from License headers

Closes #5602 from rohit7195/Arrow-6812 and squashes the following commits:

f7f0aa2 <Rohit Gupta> ARROW-6812:  Fix License header

Authored-by: Rohit Gupta <rohit@dremio.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>

Author: rohit7195

java/flight/pom.xml

@@ -1,11 +1,14 @@
 <?xml version="1.0"?>
-<!-- Copyright (C) 2017-2018 Dremio Corporation 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. -->
+<!-- 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. -->
 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <parent>

java/vector/src/main/java/org/apache/arrow/util/AutoCloseables.java

@@ -1,6 +1,4 @@
 /**
- * Portions Copyright (C) 2017-2018 Dremio Corporation
- *
  * 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.

java/vector/src/main/java/org/apache/arrow/util/Collections2.java

@@ -1,6 +1,4 @@
 /**
- * Portions Copyright (C) 2017-2018 Dremio Corporation
- *
  * 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.