staging: wilc1000: Delete undefined DEBUG_MODE and it's related codes

This patch removes undefined DEBUG_MODE and it's related codes.
We won't use this at the moment.

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