staging: wilc1000: remove unused struct tstrWidJoinReqExt

This patch removes struct tstrWidJoinReqExt because it's not used.

Signed-off-by: Leo Kim <leo.kim@atmel.com>
Signed-off-by: Tony Cho <tony.cho@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>