Update or delete UserViewModelProtocol

[BK-Teisrud]

In the current implementation of the application, all ViewModels are based on UserViewModelProtocol.

UserViewModel.swift contains only one method. It is the reset method.

protocol UserViewModelProtocol: ObservableObject{
    //var user: User {get set}
    func reset()
}

In all ViewModels (UserViewModel, StudentViewModel, TeacherViewModel and AdminViewModel), the reset method is implemented as an empty method.

func reset() {
        
}

We need to update UserViewModelProtocol.swift or just remove it completely. It is of no use as it is implemented today