Delete a broken threading.local example (GH-5870)

Delete a broken threading.local example (GH-5870)

This code never did anything correct or useful. The class attribute will never be affected, and the condition will never be true.
(cherry picked from commit 5fb632e83136399bad9427ee23ec8b771695290a)

Co-authored-by: Aaron Gallagher <habnabit@users.noreply.github.com>