Router.map leaks if invoked during the lifecycle of an Application Instance

Prior to FastBoot, this bug wasn't obvious.

The callback passed into `Router.map` ultimately ends up on an array: `EmberRouter.constructor.dslCallbacks`. They are then enumerated over at runtime and called when the router is initialized (per app instance). So, each request ends up pushing a new closure function that never gets cleaned up and invoked in subsequent requests.

The traditional way of defining routes, upfront and once, does not have this issue. It's only if you begin to register routes at any point during the app instance (for example, within an instance-initializer).

Cross-referencing for more details: https://github.com/emberjs/ember.js/issues/13840