env: Remove misuse of env is nowhere leftover

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 leftover of
misuse of the env is nowhere driver as default environment.

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