*: make GNU licensing statement forms more regular

This change retains "or later" state! No licensing _changes_ here,
only form is adjusted (article, space between "GPL" and "v2" and so on).

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

printutils/Kbuild.src

@@ -1,6 +1,6 @@
 # Makefile for busybox
 #
-# Licensed under the GPL v2, see the file LICENSE in this tarball.
+# Licensed under GPLv2, see file LICENSE in this source tree.
 
 lib-y :=
 

printutils/lpd.c

@@ -4,7 +4,7 @@
  *
  * Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com>
  *
- * Licensed under GPLv2, see file LICENSE in this tarball for details.
+ * Licensed under GPLv2, see file LICENSE in this source tree.
  */
 
 /*

printutils/lpr.c

@@ -7,7 +7,7 @@
  * Original idea and code:
  *      Walter Harms <WHarms@bfs.de>
  *
- * Licensed under GPLv2, see file LICENSE in this tarball for details.
+ * Licensed under GPLv2, see file LICENSE in this source tree.
  *
  * See RFC 1179 for protocol description.
  */