Behavior methods and finders should be removed when the behavior is removed from the table.

While testing I realised that my previous pull request did not clear methods and finders when a behavior was unloaded. This corrects it.

It was necessary to create a `remove()` in the BehaviorRegistry, otherwise the `set()` method would remove the previously added methods and thereby break tests that used `set()` to load mocks (At the very least, possibly other places)