powerpc/mpc85xx: socrates: Remove misuse of env is nowhere driver

When using a list of writeable variables, the initial values come from
the built-in default environment since commit 5ab81058
("env: Complete generic support for writable list"). Remove unnecessary
misuse of the env is nowhere driver as default environment.

Signed-off-by: Stefan Herbrechtsmeier <stefan.herbrechtsmeier@weidmueller.com>