qemugdb: fix licensing

qemu-gdb.py was committed after 2012-01-13, so the notice about
GPL v2-only contributions does not apply.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/scripts/qemugdb/mtree.py b/scripts/qemugdb/mtree.py
index e6791b7..3030a60 100644
--- a/scripts/qemugdb/mtree.py
+++ b/scripts/qemugdb/mtree.py
@@ -7,11 +7,8 @@
 # Authors:
 #  Avi Kivity <avi@redhat.com>
 #
-# This work is licensed under the terms of the GNU GPL, version 2.  See
-# the COPYING file in the top-level directory.
-#
-# Contributions after 2012-01-13 are licensed under the terms of the
-# GNU GPL, version 2 or (at your option) any later version.
+# This work is licensed under the terms of the GNU GPL, version 2 or
+# later.  See the COPYING file in the top-level directory.
 
 # 'qemu mtree' -- display the memory hierarchy