This variable is declared as a global in most environment location
drivers. But it is not used outside the drivers and most of the
declarations are unnecessary.

Also some drivers call free() on env_ptr which seems wrong since it is
not in the heap.

Drop the variable where possible, and all calls to free().

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>