[videosink] Refactor Renderer::init()
[videosink] Refactor Renderer::init()

The first argument, the target ClutterActor was both unneeded and still
reachable from the sink.

ystreet/clutter-gst,lubosz/clutter-gst,GNOME/clutter-gst,skinkie/clutter-gst,ystreet/clutter-gst,lubosz/clutter-gst,lubosz/clutter-gst,skinkie/clutter-gst,ystreet/clutter-gst,GNOME/clutter-gst,ystreet/clutter-gst,GNOME/clutter-gst,GNOME/clutter-gst,skinkie/clutter-gst