env: Do not make CONFIG_EXTRA_ENV_TEXT and CONFIG_EXTRA_ENV_SETTINGS conflict

Largely, the use of CONFIG_EXTRA_ENV_SETTINGS can be migrated directly
to come from CONFIG_EXTRA_ENV_TEXT.  The biggest case that cannot easily
be migrated is distro_bootcmd support.  Rather than block migration on
this, remove the #error here so that we can being moving forward.

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