staging: rtl8192u: remove unused code from cmpk_message_handle_tx()

The file r819xU_cmdpkt.c includes header r8192U.h which defines RTL8192U.
This patch removes from cmpk_message_handle_tx() the part of the code that
is never used because it resides outside the header guard #ifdef RTL8192U.

Signed-off-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>