dbus: drop unused group netdev

dbus: drop unused group netdev

The whole D-Bus source has no reference to the netdev group. It
seems that the netdev group is nowhere used. Early avahi package
versions used this group for the D-Bus specific rules. However,
today avahi uses --with-avahi-priv-access-group=adm and hence
uses the adm group for its D-Bus policy rules.

If a package is using the netdev group in its D-Bus policy rules,
that package should add the group instead.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>