staging: brcm80211: remove function prototypes from wl_export.h

The include file wl_export.h contained several function prototypes
(and one macro defintion) that were not used or implemented within
the driver.

Reviewed-by: Brett Rudley <brudley@broadcom.com>
Reviewed-by: Henry Ptasinski <henryp@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>