remove unused file

deltachat-ios/ViewModel/GroupDetailViewModel.swift

@@ -1,9 +0,0 @@
-//
-//  GroupDetailViewModel.swift
-//  deltachat-ios
-//
-//  Created by Macci on 06.03.20.
-//  Copyright © 2020 Jonas Reinsch. All rights reserved.
-//
-
-import Foundation