oniro-linux.conf: Rethink how DISTRO_FEATURES/IMAGE_FEATURES are defined

Right now, we do a remove in DISTRO_FEATURES. While we don't necessarily support those features, due to the finality of :remove, we force our endusers to not use them either.

By moving DISTRO_FEATURES:remove to DEFAULT_DISTRO_FEATURES:remove, we enable endusers to turn those DISTRO_FEATURES back on if needed.

We also move IMAGE_FEATURES from a distro level variable to the image. IMAGE_FEATURES should generally be put in image recipes per YP docs. This also gives end users a way to use Oniro and work around our :remove defaults.

Signed-off-by: Eilís Ní Fhlannagáin pidge@pidge.org