barco: drop unsupported board configuration

The barco board appears to be unmaintained since it was added about 5
years ago. The environment location has probably never been correct.
Drop it.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Marc Leeman <marc.leeman@barco.com>
Acked-by: Stefan Roese <sr@denx.de>