wl1251: remove accidentally added wl1251_netlink.c

Commit "wl1251: add wl1251 prefix to all 1251 files" accidentally added
wl1251_netlink.c which contains a private netlink interface.

Signed-off-by: Kalle Valo <kalle.valo@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>