gobex: Add SPDX License Identifier

gobex: Add SPDX License Identifier

This patch adds SPDX License Identifier and removes the license text.

-------------------------------------
       License            COUNT
-------------------------------------
 GPL-2.0-or-later     :     12

License: GPL-2.0-or-later
   gobex/gobex-defs.h
   gobex/gobex-transfer.c
   gobex/gobex.c
   gobex/gobex-apparam.h
   gobex/gobex-header.h
   gobex/gobex-header.c
   gobex/gobex.h
   gobex/gobex-packet.h
   gobex/gobex-defs.c
   gobex/gobex-debug.h
   gobex/gobex-apparam.c
   gobex/gobex-packet.c

Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>