staging: wilc1000: remove useless define PHY_802_11n

The define PHY_802_11n is useless because wilc1000 support 802.11n as always.
Remove PHY_802_11n and it related code.

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>