staging: brcm80211: remove dead client interrupt code from brcmfmac

In fullmac, brcmf_sdcard_intr_enable/disable is a legacy layer and
doesn't really enable/disable any interrupt. This patch removes the
corresponding code.

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>