brcm80211: smac: remove unused code for 40MHz channels

This code has been kept around in anticipation of adding support for
40MHz channels, but subsequent patches to better integrate with mac80211
regulatory support will render it completely broken. Therefore we should
go ahead and remove it.

Keep these changes separate from other cleanup patches in order to make
it easier to resurrect 40MHz channel support at some point in the
future.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>