Revert "env: Make _init() expect _INVALID when _IS_NOWHERE"

Upon further discussion, this is not required now.

This reverts commit f6bc5d17.

Link: https://lore.kernel.org/r/ebd92337-669a-9a0a-0af3-d06b957f3b40@denx.de/


Signed-off-by: Tom Rini <trini@konsulko.com>