doc(application factory): fix the doc

fixes #1586 

Remove some outdated doc.

The top-most comment in this file refer to the application-app library which has [an up to date documentation on static vs dynamic apps](https://github.com/angular/angular.dart/blob/0fbd007e0910fe421a9dc8b84da2ea92b2c7b768/lib/application.dart#L1).



/cc @vmendi