oniro-linux.conf: Make the distro stand alone as opposed to poky-based

Currently, the Linux Oniro distro configuration is based on poky. We
plan to simplify the build setup by using oe-core and bitbake directly
so we remove this distro dependency by making it a standalone distro
configuration.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>