staging: ath6kl: remove-typedef ATHBT_FILTER_INSTANCE

We mark this as unused as well, given that I find no users,
at a later time we can determine to nuke this or not...

Cc: Naveen Singh <naveen.singh@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>