gnome-control-center: reduce 'dbus-x11' dependency to 'dbus'
    
    Back in the days a dependency on 'dbus-x11' was required to
    automatically start a session bus when Xorg starts up. This is no
    longer the case, as the 'dbus' package now always provides a system-
    and user-bus to its dependents (currently via systemd units).
    
    Lets reduce the 'dbus-x11' dependency to 'dbus', so we no longer
    explicitly pull in 'dbus-daemon' recursively, but can safely support
    other bus providers that don't support the legacy X11 startup scripts
    (in particular dbus-broker).
    
    Signed-off-by: David Herrmann <dh.herrmann@gmail.com>