overlay: move init/free to the context of the render thread

This is done to allow overlays to make use of the renderer during
init/free.

client/renderers/EGL/egl.c

@@ -280,7 +280,6 @@ static void egl_deinitialize(LG_Renderer * renderer)
   if (this->imgui)
     ImGui_ImplOpenGL3_Shutdown();
 
-  app_unregisterGraph(this->importGraph);
   ringbuffer_free(&this->importTimings);
 
   egl_desktopFree(&this->desktop);