Remove unused _cogl_swap_buffers_notify

Recently _cogl_swap_buffers_notify was added (in 142b229c5c) so that
Cogl would be notified when Clutter performs a swap buffers request for
a given onscreen framebuffer. It was expected this would be required for
the recent cogl_read_pixel optimization that was implemented (ref
1bdb0e6e98) but in the end it wasn't used.

Since it wasn't used in the end this patch removes the API.

cogl/cogl-framebuffer-private.h

@@ -212,9 +212,6 @@ _cogl_framebuffer_flush_journal (CoglFramebuffer *framebuffer);
 void
 _cogl_framebuffer_flush_dependency_journals (CoglFramebuffer *framebuffer);
 
-void
-_cogl_framebuffer_swap_notify (CoglFramebuffer *framebuffer);
-
 gboolean
 _cogl_framebuffer_try_fast_read_pixel (CoglFramebuffer *framebuffer,
                                        int x,

cogl/cogl-framebuffer.c

@@ -457,11 +457,6 @@ _cogl_framebuffer_clear (CoglFramebuffer *framebuffer,
                              cogl_color_get_alpha_float (color));
 }
 
-void
-_cogl_framebuffer_swap_notify (CoglFramebuffer *framebuffer)
-{
-}
-
 int
 _cogl_framebuffer_get_width (CoglFramebuffer *framebuffer)
 {

cogl/cogl.c

@@ -1109,14 +1109,3 @@ _cogl_error_quark (void)
 {
   return g_quark_from_static_string ("cogl-error-quark");
 }
-
-/* Until Cogl becomes responsible for handling swap-buffer requests
- * this API is used by Clutter to notify us when it issues a
- * swap-buffer on our behalf. */
-void
-_cogl_swap_buffers_notify (void)
-{
-  _COGL_GET_CONTEXT (ctx, NO_RETVAL);
-
-  _cogl_framebuffer_swap_notify (_cogl_get_draw_buffer ());
-}

cogl/cogl.h

@@ -1280,9 +1280,6 @@ _cogl_driver_error_quark (void);
 void
 _cogl_onscreen_clutter_backend_set_size (int width, int height);
 
-void
-_cogl_swap_buffers_notify (void);
-
 CoglFramebuffer *
 _cogl_get_draw_buffer (void);