staging: brcm80211: cleanup unnecessary functions from wlc_ampdu.c

Couple of functions are not used or empty and have been removed.

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