Edit Fluentd license info so GitHub recognizes it

GitHub uses a library called Licensee to identify a project's license
type. It shows this information in the status bar and via the API if it
can unambiguously identify the license.

This commit removes the COPYING file (which duplicates info that's
already included in LICENSE), so that the license type identification
(as Apache 2.0) will succeed.

Signed-off-by: Andrea Kao <[email protected]>

Author: eirinikos

COPYING

@@ -187,7 +187,7 @@
       same "printed page" as the copyright notice for easier
       identification within third-party archives.
 
-   Copyright [yyyy] [name of copyright owner]
+   Copyright 2011-2018 Fluentd Authors
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.

LICENSE

@@ -73,7 +73,7 @@ Many enterprises run Fluentd in production to handle all of their logging needs.
 - Slack / Community: https://slack.fluentd.org
 - Newsletters: https://www.fluentd.org/newsletter_signup
 - Author: Sadayuki Furuhashi
-- Copyright: (c) 2011 FURUHASHI Sadayuki
+- Copyright: 2011-2018 Fluentd Authors
 - License: Apache License, Version 2.0
 
 ## Contributors: