Remove redundant "Dual License" from debian/copyright

In machine-readable format, "or" already mean dual licensed.
Fixes harmless but annoying Lintian warning:
 space-in-std-shortname-in-dep5-copyright x11 dual license

debian/changelog

@@ -8,6 +8,8 @@ linux (4.17~rc4-1~exp1) UNRELEASED; urgency=medium
   * Add new "pkg.linux.nosource" build profile that disables building the
     linux-source-* package, and a "[packages] source" option for the
     debian/config/defines file that defines the default behaviour.
+  * Remove redundant "Dual License" from debian/copyright to fix Lintian
+    source warning "space-in-std-shortname-in-dep5-copyright".
 
   [ John Paul Adrian Glaubitz ]
   * [m68k] Enable CONFIG_PATA_GAYLE as module.

debian/copyright

@@ -73,7 +73,7 @@ Files:
  include/dt-bindings/dma/sun4i-a10.h
  include/dt-bindings/pinctrl/sun4i-a10.h
  include/dt-bindings/reset/sun*.h
-License: GPL-2+ or X11 Dual License
+License: GPL-2+ or X11
 
 Files: drivers/crypto/vmx/*.pl
 Copyright: 2006,2014 Andy Polyakov <appro@openssl.org>
@@ -217,7 +217,7 @@ License: LGPL-2.1
  On Debian systems, the complete text of the GNU Lesser General Public
  License version 2.1 can be found in `/usr/share/common-licenses/LGPL-2.1'.
 
-License: GPL-2+ or X11 Dual License
+License: GPL-2+ or X11
  This file is dual-licensed: you can use it either under the terms
  of the GPL or the X11 license, at your option. Note that this dual
  licensing only applies to this file, and not this project as a