Blender Git Loki

Nodes: Remove unnecessary node tree socket tagging

`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