Hide clutter_gst_find_renderer_by_format()
Hide clutter_gst_find_renderer_by_format()

This function was never intended to be a public symbol, mark it static
as it should have been done since its introduction.

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