Remove selection color from the base

Use indirect access to it via object.

It was already flushing from base to object, now we can avoid such flushing.

Still weird to have selection color filled in by dependency graph, but now
there is no synchronization going on at least.

source/blender/depsgraph/intern/builder/deg_builder_nodes_scene.cc

@@ -81,12 +81,12 @@ void DepsgraphNodeBuilder::build_scene(Main *bmain, Scene *scene)
 	}
 
 	/* scene objects */
-	int selection_color = 1;
+	int select_color = 1;
 	for (SceneLayer *sl = (SceneLayer *)scene->render_layers.first; sl; sl = sl->next) {
 		for (Base *base = (Base *)sl->object_bases.first; base; base = base->next) {
 			/* object itself */
 			build_object(scene, base->object);
-			base->selcol = selection_color++;
+			base->object->select_color = select_color++;
 		}
 	}