Sessions and Calls should be destroyed in CHANNEL_DESTROY?

[goodboy]

Not sure why (other then perf?) we aren't just destroying all Session and Call models in a CHANNEL_DESTROY event handler? It seems to always come after CHANNEL_HANGUP. This should also simplify the logic int he CDR app here such that we won't need to make temp bindings to sessions on the call instance.

[goodboy]

Just plugged in a callback and ran the unit tests. Seems to be fine? It'd be interesting to see the effects once we have proper benchmarking tests in place.