Cleanup/simplify copyright info

Historically we have been (more-or-less consistently, sometimes forgetting
some files) updating the end year of the copyright statements at the
beginning of a new year.

We're naturally not alone in that.  Recently this was discussed in curl, and
it turns out that copyright years are not really required:

https://daniel.haxx.se/blog/2023/01/08/copyright-without-years/

So drop the years and simplify the copyright statements.  While we're at it,
also ensure the same syntax (capital C, email address) is used everywhere.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

Makefile

@@ -1,8 +1,6 @@
 # Makefile for buildroot
 #
-# Copyright (C) 1999-2005 by Erik Andersen <andersen@codepoet.org>
-# Copyright (C) 2006-2014 by the Buildroot developers <buildroot@uclibc.org>
-# Copyright (C) 2014-2020 by the Buildroot developers <buildroot@buildroot.org>
+# Copyright (C) the Buildroot developers <buildroot@buildroot.org>
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by

docs/manual/manual.txt

@@ -12,7 +12,7 @@ It is licensed under the GNU General Public License, version 2. Refer to the
 http://git.buildroot.org/buildroot/tree/COPYING?id={sys:git rev-parse HEAD}[COPYING]
 file in the Buildroot sources for the full text of this license.
 
-Copyright (C) 2004-2020 The Buildroot developers
+Copyright (C) The Buildroot developers <buildroot@buildroot.org>
 
 image::logo.png[]
 

docs/website/copyright.txt

@@ -1,7 +1,7 @@
 
 The code and graphics on this website (and it's mirror sites, if any) are
-Copyright (c) 1999-2005 by Erik Andersen, 2006-2020 The Buildroot
-developers. All rights reserved.
+Copyright (C) The Buildroot developers <buildroot@buildroot.org>.  All
+rights reserved.
 
 Documents on this Web site including their graphical elements, design, and
 layout are protected by trade dress and other laws and MAY BE COPIED OR