Revert "event: Add App event variant for custom events"

This reverts commit 7b93a513af105ec3509c286b892b98417f413b03.
Fix bug in union app constructor

The partial application point was not being respected, i.e.,
applications were being reinitialized on every event.
Change handler API

Now a hander returns to things: a Pipe reader to any events that the app
may produce, as well as an event handler that may update the policy.
Add update event

Indicates that any stateful updates that apps have made should now be
reflected in the policy
Forget mappings in learning switch after 30 seconds