ERIC: drop unsupported board configuration

The ERIC board appears to be unmaintained for more than 9 years. The
environment location has probably never been correct, and has been
definitely broken since for at least a year.  Drop it.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Stefan Roese <sr@denx.de>
Cc: Swen Anderson <sand@peppercon.de>
Acked-by: Stefan Roese <sr@denx.de>