cogl-framebuffer: Remove all dependencies after a flush

After a dependent framebuffer is added to a framebuffer it was never
getting removed. Once the journal for a framebuffer is flushed we no
longer depend on any framebuffers so the list should be cleared. This
was causing leaks of offscreens and textures.

clutter/cogl/cogl/cogl-framebuffer.c

@@ -597,6 +597,7 @@ _cogl_framebuffer_flush_dependency_journals (CoglFramebuffer *framebuffer)
   GList *l;
   for (l = framebuffer->deps; l; l = l->next)
     _cogl_framebuffer_flush_journal (l->data);
+  _cogl_framebuffer_remove_all_dependencies (framebuffer);
 }
 
 static inline void