release-0bed230f: Remove TigonTokenObserver usage in Loom

Summary:
This TigonTokenObserver was added to track TigonPriority changes and cancel events. Original diffs: D10463904 (https://github.com/facebookincubator/profilo/commit/a73b5d6c67db796e290c12a9f8840a1be629e109) and D10403620

- TigonPriority tracking was removed in D34515445 but left NET_CHANGEPRI in a couple places.
- The cancel events can be obtained from TigonError instead.

Since this is the only token observer usage, will remove TigonTokenObserver in TigonSecretary next.

For future reference on how to regenerate Loom types,
```
./libraries/profilo/cpp/generated/generate_sources.sh
```

Reviewed By: mengz0, yukonfb

Differential Revision: D34821591

fbshipit-source-id: a73a934451aaf5ad1b213e25f9f5a6ab094ad791