prd-flash: rely on libubootenv instead of u-boot-fw-utils
prd-flash: rely on libubootenv instead of u-boot-fw-utils

With dunfell release, libubootenv became preferred provider (and widely the
one and only) for fw_printenv/fw_setenv. This fix follows the upstream.

Signed-off-by: Jens Rehsack <69d49c504a9219a55b8be0f905e8fe3c32ffb57f@netbsd.org>

rehsack/meta-jens,rehsack/meta-jens,rehsack/meta-jens