staging: wilc1000: remove unused functions

This patch removes unused following functions.
wilc_del_all_rx_ba_session
wilc_flush_join_req
wilc_wait_msg_queue_idle
wilc_set_mac_address

Signed-off-by: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>