staging: wilc1000: remove os_private

This patch removes unused variable os_private and delete
struct wilc_wlan_os_context_t since there is no members in it. Remove it's
related code also.

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