Bug #40842: Don't use sets in_full_teardown

The maze will still try to use marked circuits, because the maze does what it wants. But at least we can stop from looking into the conflux data associated with them.

changes/bug40842

+  o Minor bugfixes (conflux):
+    - Prevent non-fatal assert stacktrace caused by using conflux
+      sets during their teardown process. Fixes bug 40842;
+      bugfix on 0.4.8.1-alpha.