staging: brcm80211: removed unused softmac code after macro cleanup

Since the macro's IS_MCS(0), RSPEC_STF(0) and PHY_TXC1_MODE_SISO all
expand to 0, inactive code could be removed.

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