staging: wilc1000: remove host_int_add_tx_gtk declaration

This patch removes host_int_add_tx_gtk declaration that is defined in
host_interface.h file. It can not find any host_int_add_tx_gtk
function definition in this driver so just remove it.

Signed-off-by: Chaehyun Lim <chaehyun.lim@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>