staging: brcm80211: Remove unused structure.

Remove the wl_assoc_info_t structure.  It's never used, and depends on
structures defined in other header files that can now also be cleaned up.

Signed-off-by: Henry Ptasinski <henryp@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>