env: Remove useless CONFIG_ENV_SIZE_REDUND and fix ENV_IS_REDUND check

We have CONFIG_ENV_SIZE_IS_REDUND but don't really use it.  We have one
board where we can simply multiple CONFIG_ENV_SIZE by two for the same
result.  The other place where we could but were not previously using
this is for where env_internal.h checks for if we should set
ENV_IS_EMBEDDED.  This seems like the most likely use, historically, of
the variable, but it was not used.  Add logic to check for this now.

Cc: Wolfgang Denk <wd@denx.de>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>