`SOCK_IN_USE` is now set in `update_socket_used_tags` in `node_tree_update.cc` when a node tree is changed. It doesn't need to run every single redraw. Removing this results in a small speedup of 0.4 ms when drawing a tree with about 4000 nodes (from about 70 ms total). Differential Revision: https://developer.blender.org/D13645