Blackfin: bf561-acvilon: drop unused env redund define

The SPI env code didn't support redundant environments until recently, but
this code was written before that.  Since it has never been tested (and
currently causes a build failure), simply punt it.  If the functionality
is actually desired, it can be re-added once it has been tested.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>