not way to delete and add Internal users from projects

There was never a way to add Internal users from the Project management page.

This is by design to avoid confusion. Internal users have access to ALL of your company's projects - you do not want to give access to someone who isn't an internal employee of your company or doesn't need access to all projects.

Internal users can be added from the Organization settings page, as its always been.

In the old version bugtracker I could manage internal people from the project.

it is very uncomfortably. I have to add all internal people (about 50 users) in project but i need only in 5 people. Furthermore I have to spent time on choose whom I want to assign an error. each time creating new bug http://screencast.com/t/5D1zIejeUFr

There was a way to add and delete users.

As Scherbakovden said if not everyone in the organisation would work on every project. There are only certain users working a project. The account manager should be able to add or delete internal user for a project